{"id":212,"date":"2021-06-04T18:10:08","date_gmt":"2021-06-04T18:10:08","guid":{"rendered":"https:\/\/courses.lumenlearning.com\/gsu-precalculus\/chapter\/non-right-triangles-law-of-cosines\/"},"modified":"2023-09-18T19:11:44","modified_gmt":"2023-09-18T19:11:44","slug":"non-right-triangles-law-of-cosines","status":"publish","type":"chapter","link":"https:\/\/courses.lumenlearning.com\/gsu-precalculus\/chapter\/non-right-triangles-law-of-cosines\/","title":{"raw":"3.2 Law of Cosines","rendered":"3.2 Law of Cosines"},"content":{"raw":"<div class=\"bcc-box bcc-highlight\">\r\n<h3>Learning Outcomes<\/h3>\r\n<ul>\r\n \t<li>Use the Law of Cosines to solve oblique triangles.<\/li>\r\n \t<li>Solve applied problems using the Law of Cosines.<\/li>\r\n \t<li>Use Heron\u2019s formula to \ufb01nd the area of a triangle.<\/li>\r\n<\/ul>\r\n<\/div>\r\nSuppose a boat leaves port, travels 10 miles, turns 20 degrees, and travels another 8 miles as shown in Figure 1.\u00a0How far from port is the boat?\r\n\r\n[caption id=\"\" align=\"aligncenter\" width=\"487\"]<img src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/3675\/2018\/09\/27165212\/CNX_Precalc_Figure_08_02_0012.jpg\" alt=\"A triangle whose vertices are the boat, the port, and the turning point of the boat. The side between the port and the turning point is 10 mi, and the side between the turning point and the boat is 8 miles. The side between the port and the turning point is extended in a straight dotted line. The angle between the dotted line and the 8 mile side is 20 degrees.\" width=\"487\" height=\"517\" \/> <b>Figure 1<\/b>[\/caption]\r\n\r\nUnfortunately, while the Law of Sines enables us to address many non-right triangle cases, it does not help us with triangles where the known angle is between two known sides, a <strong>SAS (side-angle-side) triangle<\/strong>, or when all three sides are known, but no angles are known, a <strong>SSS (side-side-side) triangle<\/strong>. In this section, we will investigate another tool for solving oblique triangles described by these last two cases.\r\n<h2>Using the Law of Cosines to Solve Oblique Triangles<\/h2>\r\nThe tool we need to solve the problem of the boat\u2019s distance from the port is the <strong>Law of Cosines<\/strong>, which defines the relationship among angle measurements and side lengths in oblique triangles. Three formulas make up the Law of Cosines. At first glance, the formulas may appear complicated because they include many variables. However, once the pattern is understood, the Law of Cosines is easier to work with than most formulas at this mathematical level.\r\n\r\nUnderstanding how the Law of Cosines is derived will be helpful in using the formulas. The derivation begins with the <strong>Generalized Pythagorean Theorem<\/strong>, which is an extension of the <strong>Pythagorean Theorem<\/strong> to non-right triangles. Here is how it works: An arbitrary non-right triangle [latex]ABC[\/latex] is placed in the coordinate plane with vertex [latex]A[\/latex] at the origin, side [latex]c[\/latex] drawn along the <em>x<\/em>-axis, and vertex [latex]C[\/latex] located at some point [latex]\\left(x,y\\right)[\/latex] in the plane, as illustrated in Figure 2. Generally, triangles exist anywhere in the plane, but for this explanation we will place the triangle as noted.\r\n\r\n[caption id=\"\" align=\"aligncenter\" width=\"487\"]<img src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/3675\/2018\/09\/27165215\/CNX_Precalc_Figure_08_02_0022.jpg\" alt=\"A triangle A B C plotted in quadrant 1 of the x,y plane. Angle A is theta degrees with opposite side a, angles B and C, with opposite sides b and c respectively, are unknown. Vertex A is located at the origin (0,0), vertex B is located at some point (x-c, 0) along the x-axis, and point C is located at some point in quadrant 1 at the point (b times the cos of theta, b times the sin of theta). \" width=\"487\" height=\"266\" \/> <b>Figure 2<\/b>[\/caption]\r\n\r\nWe can drop a perpendicular from [latex]C[\/latex] to the <em>x-<\/em>axis (this is the altitude or height). Recalling the basic <strong>trigonometric identities<\/strong>, we know that\r\n<div style=\"text-align: center;\">[latex]\\cos \\theta =\\frac{x\\text{(adjacent)}}{b\\text{(hypotenuse)}}\\text{ and }\\sin \\theta =\\frac{y\\text{(opposite)}}{b\\text{(hypotenuse)}}[\/latex]<\/div>\r\nIn terms of [latex]\\theta ,\\text{ }x=b\\cos \\theta [\/latex] and [latex]y=b\\sin \\theta .\\text{ }[\/latex] The [latex]\\left(x,y\\right)[\/latex] point located at [latex]C[\/latex] has coordinates [latex]\\left(b\\cos \\theta ,b\\sin \\theta \\right)[\/latex]. Using the side [latex]\\left(x-c\\right)[\/latex] as one leg of a right triangle and [latex]y[\/latex] as the second leg, we can find the length of hypotenuse [latex]a[\/latex] using the Pythagorean Theorem. Thus,\r\n<div style=\"text-align: center;\">[latex]\\begin{align} {a}^{2}&amp;={\\left(x-c\\right)}^{2}+{y}^{2} \\\\ &amp;={\\left(b\\cos \\theta -c\\right)}^{2}+{\\left(b\\sin \\theta \\right)}^{2} &amp;&amp; \\text{Substitute }\\left(b\\cos \\theta \\right)\\text{ for}x\\text{and }\\left(b\\sin \\theta \\right)\\text{for }y. \\\\ &amp;=\\left({b}^{2}{\\cos }^{2}\\theta -2bc\\cos \\theta +{c}^{2}\\right)+{b}^{2}{\\sin }^{2}\\theta &amp;&amp; \\text{Expand the perfect square}. \\\\ &amp;={b}^{2}{\\cos }^{2}\\theta +{b}^{2}{\\sin }^{2}\\theta +{c}^{2}-2bc\\cos \\theta &amp;&amp; \\text{Group terms noting that }{\\cos }^{2}\\theta +{\\sin }^{2}\\theta =1. \\\\ &amp;={b}^{2}\\left({\\cos }^{2}\\theta +{\\sin }^{2}\\theta \\right)+{c}^{2}-2bc\\cos \\theta &amp;&amp; \\text{Factor out }{b}^{2}. \\\\ {a}^{2}&amp;={b}^{2}+{c}^{2}-2bc\\cos \\theta &amp;&amp;{\\cos }^{2}\\theta +{\\sin }^{2}\\theta = 1 \\end{align}[\/latex]<\/div>\r\nThe formula derived is one of the three equations of the Law of Cosines. The other equations are found in a similar fashion.\r\n\r\nKeep in mind that it is always helpful to sketch the triangle when solving for angles or sides. In a real-world scenario, try to draw a diagram of the situation. As more information emerges, the diagram may have to be altered. Make those alterations to the diagram and, in the end, the problem will be easier to solve.\r\n<div class=\"textbox\">\r\n<h3>A General Note: Law of Cosines<\/h3>\r\nThe <strong>Law of Cosines<\/strong> states that the square of any side of a triangle is equal to the sum of the squares of the other two sides minus twice the product of the other two sides and the cosine of the included angle. For triangles labeled as in Figure 3, with angles [latex]\\alpha ,\\beta [\/latex], and [latex]\\gamma [\/latex], and opposite corresponding sides [latex]a,b[\/latex], and [latex]c[\/latex], respectively, the Law of Cosines is given as three equations.\r\n<p style=\"text-align: center;\">[latex]{a}^{2}={b}^{2}+{c}^{2}-2bc\\cos \\alpha[\/latex]<\/p>\r\n<p style=\"text-align: center;\">[latex]{b}^{2}={a}^{2}+{c}^{2}-2ac\\cos \\beta[\/latex]<\/p>\r\n<p style=\"text-align: center;\">[latex]{c}^{2}={a}^{2}+{b}^{2}-2ab\\cos \\gamma [\/latex]<\/p>\r\n\r\n\r\n[caption id=\"\" align=\"aligncenter\" width=\"487\"]<img src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/3675\/2018\/09\/27165217\/CNX_Precalc_Figure_08_02_003n2.jpg\" alt=\"A triangle with standard labels: angles alpha, beta, and gamma with opposite sides a, b, and c respectively.\" width=\"487\" height=\"239\" \/> <b>Figure 3<\/b>[\/caption]\r\n\r\nTo solve for a missing side measurement, the corresponding opposite angle measure is needed.\r\n\r\nWhen solving for an angle, the corresponding opposite side measure is needed. We can use another version of the Law of Cosines to solve for an angle.\r\n<p style=\"text-align: center;\">[latex]\\cos \\alpha =\\frac{{b}^{2}+{c}^{2}-{a}^{2}}{2bc}[\/latex]<\/p>\r\n<p style=\"text-align: center;\">[latex]\\cos \\beta =\\frac{{a}^{2}+{c}^{2}-{b}^{2}}{2ac}[\/latex]<\/p>\r\n<p style=\"text-align: center;\">[latex]\\cos\\gamma =\\frac{{a}^{2}+{b}^{2}-{c}^{2}}{2ab}[\/latex]<\/p>\r\n\r\n<\/div>\r\n<div class=\"textbox\">\r\n<h3>How To:\u00a0Given two sides and the angle between them (SAS), find the measures of the remaining side and angles of a triangle.<\/h3>\r\n<ol id=\"fs-id1165132949849\">\r\n \t<li>Sketch the triangle. Identify the measures of the known sides and angles. Use variables to represent the measures of the unknown sides and angles.<\/li>\r\n \t<li>Apply the Law of Cosines to find the length of the unknown side or angle.<\/li>\r\n \t<li>Apply the <strong>Law of Sines<\/strong> or Cosines to find the measure of a second angle.<\/li>\r\n \t<li>Compute the measure of the remaining angle.<\/li>\r\n<\/ol>\r\n<\/div>\r\n<div class=\"textbox shaded\">\r\n<h3>Example 1: Finding the Unknown Side and Angles of a SAS Triangle<\/h3>\r\nFind the unknown side and angles of the triangle in Figure 4.\r\n\r\n[caption id=\"\" align=\"aligncenter\" width=\"487\"]<img src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/3675\/2018\/09\/27165219\/CNX_Precalc_Figure_08_02_0042.jpg\" alt=\"A triangle with standard labels. Side a = 10, side c = 12, and angle beta = 30 degrees.\" width=\"487\" height=\"189\" \/> <b>Figure 4<\/b>[\/caption]\r\n\r\n[reveal-answer q=\"359338\"]Show Solution[\/reveal-answer]\r\n[hidden-answer a=\"359338\"]\r\n\r\nFirst, make note of what is given: two sides and the angle between them. This arrangement is classified as SAS and supplies the data needed to apply the Law of Cosines.\r\n\r\nEach one of the three laws of cosines begins with the square of an unknown side opposite a known angle. For this example, the first side to solve for is side [latex]b[\/latex], as we know the measurement of the opposite angle [latex]\\beta [\/latex].\r\n<p style=\"text-align: center;\">[latex]\\begin{align}&amp;{b}^{2}={a}^{2}+{c}^{2}-2ac\\cos \\beta \\\\ &amp;{b}^{2}={10}^{2}+{12}^{2}-2\\left(10\\right)\\left(12\\right)\\cos \\left({30}^{\\circ }\\right) &amp;&amp; \\text{Substitute the measurements for the known quantities}. \\\\ &amp;{b}^{2}=100+144 - 240\\left(\\frac{\\sqrt{3}}{2}\\right)&amp;&amp; \\text{Evaluate the cosine and begin to simplify}. \\\\ &amp;{b}^{2}=244 - 120\\sqrt{3} \\\\ &amp;b=\\sqrt{244 - 120\\sqrt{3}}&amp;&amp; \\text{Use the square root property}. \\\\ &amp;b\\approx 6.013 \\end{align}[\/latex]<\/p>\r\nBecause we are solving for a length, we use only the positive square root. Now that we know the length [latex]b[\/latex], we can use the Law of Sines to fill in the remaining angles of the triangle. Solving for angle [latex]\\alpha [\/latex], we have\r\n<p style=\"text-align: center;\">[latex]\\begin{align}&amp;\\frac{\\sin \\alpha }{a}=\\frac{\\sin \\beta }{b} \\\\ &amp;\\frac{\\sin \\alpha }{10}=\\frac{\\sin \\left(30^\\circ \\right)}{6.013} \\\\ &amp;\\sin \\alpha =\\frac{10\\sin \\left(30^\\circ \\right)}{6.013}&amp;&amp; \\text{Multiply both sides of the equation by 10}. \\\\ &amp;\\alpha ={\\sin }^{-1}\\left(\\frac{10\\sin \\left(30^\\circ \\right)}{6.013}\\right)&amp;&amp; \\text{Find the inverse sine of }\\frac{10\\sin \\left(30^\\circ \\right)}{6.013}. \\\\ &amp;\\alpha \\approx 56.3^\\circ \\end{align}[\/latex]<\/p>\r\nThe other possibility for [latex]\\alpha [\/latex] would be [latex]\\alpha =180^\\circ -56.3^\\circ \\approx 123.7^\\circ [\/latex]. In the original diagram, [latex]\\alpha [\/latex] is adjacent to the longest side, so [latex]\\alpha [\/latex] is an acute angle and, therefore, [latex]123.7^\\circ [\/latex] does not make sense. Notice that if we choose to apply the <strong>Law of Cosines<\/strong>, we arrive at a unique answer. We do not have to consider the other possibilities, as cosine is unique for angles between [latex]0^\\circ [\/latex] and [latex]180^\\circ [\/latex]. Proceeding with [latex]\\alpha \\approx 56.3^\\circ [\/latex], we can then find the third angle of the triangle.\r\n<p style=\"text-align: center;\">[latex]\\gamma =180^\\circ -30^\\circ -56.3^\\circ \\approx 93.7^\\circ [\/latex]<\/p>\r\nThe complete set of angles and sides is\r\n<p style=\"text-align: center;\">[latex]\\begin{align}&amp;\\alpha \\approx 56.3^\\circ &amp;&amp; a=10\\\\ &amp;\\beta =30^\\circ &amp;&amp; b\\approx 6.013\\\\ &amp;\\gamma \\approx 93.7^\\circ &amp;&amp; c=12 \\end{align}[\/latex]<\/p>\r\n[\/hidden-answer]\r\n\r\n<\/div>\r\n<div class=\"bcc-box bcc-success\">\r\n<h3>Try It<\/h3>\r\nFind the missing side and angles of the given triangle: [latex]\\alpha =30^\\circ ,b=12,c=24[\/latex].\r\n\r\n[reveal-answer q=\"885435\"]Show Solution[\/reveal-answer]\r\n[hidden-answer a=\"885435\"]\r\n\r\n[latex]a\\approx 14.9,\\beta \\approx 23.8^\\circ ,\\gamma \\approx 126.2^\\circ [\/latex].\r\n\r\n[\/hidden-answer]\r\n\r\n<\/div>\r\n<div class=\"textbox key-takeaways\">\r\n<h3>Try It<\/h3>\r\n[ohm_question hide_question_numbers=1 height=\"270\"]174837[\/ohm_question]\r\n\r\n<\/div>\r\n<div class=\"textbox shaded\">\r\n<h3>Example 2: Solving for an Angle of a SSS Triangle<\/h3>\r\nFind the angle [latex]\\alpha [\/latex] for the given triangle if side [latex]a=20[\/latex], side [latex]b=25[\/latex], and side [latex]c=18[\/latex].\r\n\r\n[reveal-answer q=\"211238\"]Show Solution[\/reveal-answer]\r\n[hidden-answer a=\"211238\"]\r\n\r\nFor this example, we have no angles. We can solve for any angle using the Law of Cosines. To solve for angle [latex]\\alpha [\/latex], we have\r\n<p style=\"text-align: center;\">[latex]\\begin{align} &amp;{a}^{2}={b}^{2}+{c}^{2}-2bc\\cos \\alpha \\\\ &amp;{20}^{2}={25}^{2}+{18}^{2}-2\\left(25\\right)\\left(18\\right)\\cos \\alpha&amp;&amp; \\text{Substitute the appropriate measurements}. \\\\ &amp;400=625+324 - 900\\cos \\alpha&amp;&amp; \\text{Simplify in each step}. \\\\ &amp;400=949 - 900\\cos \\alpha \\\\ &amp;-549=-900\\cos \\alpha&amp;&amp; \\text{Isolate cos }\\alpha . \\\\ &amp;\\frac{-549}{-900}=\\cos \\alpha \\\\ &amp;0.61\\approx \\cos \\alpha \\\\ &amp;{\\cos }^{-1}\\left(0.61\\right)\\approx \\alpha&amp;&amp; \\text{Find the inverse cosine}. \\\\ &amp;\\alpha \\approx 52.4^\\circ \\end{align}[\/latex]<\/p>\r\nSee Figure 5.\r\n\r\n[caption id=\"\" align=\"aligncenter\" width=\"487\"]<img src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/3675\/2018\/09\/27165221\/CNX_Precalc_Figure_08_02_0052.jpg\" alt=\"A triangle with standard labels. Side b =25, side a = 20, side c = 18, and angle alpha = 52.4 degrees.\" width=\"487\" height=\"266\" \/> <b>Figure 5<\/b>[\/caption]\r\n<h4>Analysis of the Solution<\/h4>\r\nBecause the inverse cosine can return any angle between 0 and 180 degrees, there will not be any ambiguous cases using this method.\r\n\r\n[\/hidden-answer]\r\n\r\n<\/div>\r\n<div class=\"bcc-box bcc-success\">\r\n<h3>Try It<\/h3>\r\nGiven [latex]a=5,b=7[\/latex], and [latex]c=10[\/latex], find the missing angles.\r\n\r\n[reveal-answer q=\"488277\"]Show Solution[\/reveal-answer]\r\n[hidden-answer a=\"488277\"]\r\n\r\n[latex]\\alpha \\approx 27.7^\\circ ,\\beta \\approx 40.5^\\circ ,\\gamma \\approx 111.8^\\circ [\/latex]\r\n\r\n[\/hidden-answer]\r\n\r\n<\/div>\r\n<div class=\"textbox key-takeaways\">\r\n<h3>Try It<\/h3>\r\n[ohm_question hide_question_numbers=1 height=\"350\"]173789[\/ohm_question]\r\n\r\n<\/div>\r\n<h2>Solving Applied Problems Using the Law of Cosines<\/h2>\r\nJust as the Law of Sines provided the appropriate equations to solve a number of applications, the Law of Cosines is applicable to situations in which the given data fits the cosine models. We may see these in the fields of navigation, surveying, astronomy, and geometry, just to name a few.\r\n<div class=\"textbox shaded\">\r\n<h3>Example 3: Using the Law of Cosines to Solve a Communication Problem<\/h3>\r\nOn many cell phones with GPS, an approximate location can be given before the GPS signal is received. This is accomplished through a process called triangulation, which works by using the distances from two known points. Suppose there are two cell phone towers within range of a cell phone. The two towers are located 6000 feet apart along a straight highway, running east to west, and the cell phone is north of the highway. Based on the signal delay, it can be determined that the signal is 5050 feet from the first tower and 2420 feet from the second tower. Determine the position of the cell phone north and east of the first tower, and determine how far it is from the highway.\r\n\r\n[reveal-answer q=\"960347\"]Show Solution[\/reveal-answer]\r\n[hidden-answer a=\"960347\"]\r\n\r\nFor simplicity, we start by drawing a diagram similar to Figure 6\u00a0and labeling our given information.\r\n\r\n[caption id=\"\" align=\"aligncenter\" width=\"487\"]<img src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/3675\/2018\/09\/27165224\/CNX_Precalc_Figure_08_02_0062.jpg\" alt=\"A triangle formed between the two cell phone towers located on am east to west highway and the cellphone between and north of them. The side between the two towers is 6000 feet, the side between the left tower and the phone is 5050 feet, and the side between the right tower and the phone is 2420 feet. The angle between the 5050 and 6000 feet sides is labeled theta.\" width=\"487\" height=\"199\" \/> <b>Figure 6<\/b>[\/caption]\r\n\r\nUsing the Law of Cosines, we can solve for the angle [latex]\\theta [\/latex]. Remember that the Law of Cosines uses the square of one side to find the cosine of the opposite angle. For this example, let [latex]a=2420,b=5050[\/latex], and [latex]c=6000[\/latex]. Thus, [latex]\\theta [\/latex] corresponds to the opposite side [latex]a=2420[\/latex].\r\n<p style=\"text-align: center;\">[latex]\\begin{gathered}{a}^{2}={b}^{2}+{c}^{2}-2bc\\cos \\theta \\\\ {\\left(2420\\right)}^{2}={\\left(5050\\right)}^{2}+{\\left(6000\\right)}^{2}-2\\left(5050\\right)\\left(6000\\right)\\cos \\theta \\\\ {\\left(2420\\right)}^{2}-{\\left(5050\\right)}^{2}-{\\left(6000\\right)}^{2}=-2\\left(5050\\right)\\left(6000\\right)\\cos \\theta \\\\ \\frac{{\\left(2420\\right)}^{2}-{\\left(5050\\right)}^{2}-{\\left(6000\\right)}^{2}}{-2\\left(5050\\right)\\left(6000\\right)}=\\cos \\theta \\\\ \\cos \\theta \\approx 0.9183 \\\\ \\theta \\approx {\\cos }^{-1}\\left(0.9183\\right) \\\\ \\theta \\approx 23.3^\\circ \\end{gathered}[\/latex]<\/p>\r\nTo answer the questions about the phone\u2019s position north and east of the tower, and the distance to the highway, drop a perpendicular from the position of the cell phone, as in Figure 7.\u00a0This forms two right triangles, although we only need the right triangle that includes the first tower for this problem.\r\n\r\n[caption id=\"\" align=\"aligncenter\" width=\"487\"]<img src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/3675\/2018\/09\/27165226\/CNX_Precalc_Figure_08_02_0072.jpg\" alt=\"The triangle between the phone, the left tower, and a point between the phone and the highway between the towers. The side between the phone and the highway is perpendicular to the highway and is y feet. The highway side is x feet. The angle at the tower, previously labeled theta, is 23.3 degrees.\" width=\"487\" height=\"177\" \/> <b>Figure 7<\/b>[\/caption]\r\n\r\nUsing the angle [latex]\\theta =23.3^\\circ [\/latex] and the basic trigonometric identities, we can find the solutions. Thus\r\n<p style=\"text-align: center;\">[latex]\\begin{gathered} \\cos \\left(23.3^\\circ \\right)=\\frac{x}{5050} \\\\ x=5050\\cos \\left(23.3^\\circ \\right) \\\\ x\\approx 4638.15\\text{feet} \\\\ \\sin \\left(23.3^\\circ \\right)=\\frac{y}{5050} \\\\ y=5050\\sin \\left(23.3^\\circ \\right) \\\\ y\\approx 1997.5\\text{feet} \\end{gathered}[\/latex]<\/p>\r\nThe cell phone is approximately 4638 feet east and 1998 feet north of the first tower, and 1998 feet from the highway.\r\n\r\n[\/hidden-answer]\r\n\r\n<\/div>\r\n<div class=\"textbox shaded\">\r\n<h3>Example 4: Calculating Distance Traveled Using a SAS Triangle<\/h3>\r\nReturning to our problem at the beginning of this section, suppose a boat leaves port, travels 10 miles, turns 20 degrees, and travels another 8 miles. How far from port is the boat? The diagram is repeated here in Figure 8.\r\n\r\n[caption id=\"\" align=\"aligncenter\" width=\"487\"]<img src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/3675\/2018\/09\/27165228\/CNX_Precalc_Figure_08_02_0092.jpg\" alt=\"A triangle whose vertices are the boat, the port, and the turning point of the boat. The side between the port and the turning point is 10 mi, and the side between the turning point and the boat is 8 miles. The side between the port and the turning point is extended in a straight dotted line. The angle between the dotted line and the 8 mile side is 20 degrees.\" width=\"487\" height=\"517\" \/> <b>Figure 8<\/b>[\/caption]\r\n\r\n[reveal-answer q=\"569516\"]Show Solution[\/reveal-answer]\r\n[hidden-answer a=\"569516\"]\r\n\r\nThe boat turned 20 degrees, so the obtuse angle of the non-right triangle is the supplemental angle, [latex]180^\\circ -20^\\circ =160^\\circ [\/latex]. With this, we can utilize the Law of Cosines to find the missing side of the obtuse triangle\u2014the distance of the boat to the port.\r\n<p style=\"text-align: center;\">[latex]\\begin{align}&amp;{x}^{2}={8}^{2}+{10}^{2}-2\\left(8\\right)\\left(10\\right)\\cos \\left(160^\\circ \\right) \\\\ &amp;{x}^{2}=314.35 \\\\ &amp;x=\\sqrt{314.35} \\\\ &amp;x\\approx 17.7\\text{miles} \\end{align}[\/latex]<\/p>\r\nThe boat is about 17.7 miles from port.\r\n\r\n[\/hidden-answer]\r\n\r\n<\/div>\r\n<h2>Using Heron's Formula to Find the Area of a Triangle<\/h2>\r\nWe already learned how to find the area of an oblique triangle when we know two sides and an angle. We also know the formula to find the area of a triangle using the base and the height. When we know the three sides, however, we can use <strong>Heron\u2019s formula<\/strong> instead of finding the height. <strong>Heron of Alexandria<\/strong> was a geometer who lived during the first century A.D. He discovered a formula for finding the area of oblique triangles when three sides are known.\r\n<div class=\"textbox\">\r\n<h3>A General Note: Heron\u2019s Formula<\/h3>\r\nHeron\u2019s formula finds the area of oblique triangles in which sides [latex]a,b[\/latex], and [latex]c[\/latex] are known.\r\n<p style=\"text-align: center;\">[latex]\\text{Area}=\\sqrt{s\\left(s-a\\right)\\left(s-b\\right)\\left(s-c\\right)}[\/latex]<\/p>\r\nwhere [latex]s=\\frac{\\left(a+b+c\\right)}{2}[\/latex] is one half of the perimeter of the triangle, sometimes called the semi-perimeter.\r\n\r\n<\/div>\r\n<div class=\"textbox shaded\">\r\n<h3>Example 5: Using Heron\u2019s Formula to Find the Area of a Given Triangle<\/h3>\r\nFind the area of the triangle in Figure 9\u00a0using Heron\u2019s formula.\r\n\r\n[caption id=\"\" align=\"aligncenter\" width=\"487\"]<img src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/3675\/2018\/09\/27165230\/CNX_Precalc_Figure_08_02_0102.jpg\" alt=\"A triangle with angles A, B, and C and opposite sides a, b, and c, respectively. Side a = 10, side b - 15, and side c = 7.\" width=\"487\" height=\"134\" \/> <b>Figure 9<\/b>[\/caption]\r\n\r\n[reveal-answer q=\"256710\"]Show Solution[\/reveal-answer]\r\n[hidden-answer a=\"256710\"]\r\n\r\nFirst, we calculate [latex]s[\/latex].\r\n<p style=\"text-align: center;\">[latex]\\begin{align} s&amp;=\\frac{\\left(a+b+c\\right)}{2} \\\\ s&amp;=\\frac{\\left(10+15+7\\right)}{2}=16 \\end{align}[\/latex]<\/p>\r\nThen we apply the formula.\r\n<p style=\"text-align: center;\">[latex]\\begin{align} \\text{Area}&amp;=\\sqrt{s\\left(s-a\\right)\\left(s-b\\right)\\left(s-c\\right)} \\\\ \\text{Area}&amp;=\\sqrt{16\\left(16 - 10\\right)\\left(16 - 15\\right)\\left(16 - 7\\right)} \\\\ \\text{Area}&amp;\\approx 29.4 \\end{align}[\/latex]<\/p>\r\nThe area is approximately 29.4 square units.\r\n\r\n[\/hidden-answer]\r\n\r\n<\/div>\r\n<div class=\"bcc-box bcc-success\">\r\n<h3>Try It<\/h3>\r\nUse Heron\u2019s formula to find the area of a triangle with sides of lengths [latex]a=29.7\\text{ft},b=42.3\\text{ft}[\/latex], and [latex]c=38.4\\text{ft}[\/latex].\r\n\r\n[reveal-answer q=\"159200\"]Show Solution[\/reveal-answer]\r\n[hidden-answer a=\"159200\"]\r\n\r\nArea = 552 square feet\r\n\r\n[\/hidden-answer]\r\n\r\n<\/div>\r\n<div class=\"textbox key-takeaways\">\r\n<h3>Try It<\/h3>\r\n[ohm_question hide_question_numbers=1 height=\"350\"]149312[\/ohm_question]\r\n\r\n<\/div>\r\n<div class=\"textbox shaded\">\r\n<h3>Example 6: Applying Heron\u2019s Formula to a Real-World Problem<\/h3>\r\nA Chicago city developer wants to construct a building consisting of artist\u2019s lofts on a triangular lot bordered by Rush Street, Wabash Avenue, and Pearson Street. The frontage along Rush Street is approximately 62.4 meters, along Wabash Avenue it is approximately 43.5 meters, and along Pearson Street it is approximately 34.1 meters. How many square meters are available to the developer? See Figure 10\u00a0for a view of the city property.\r\n\r\n[caption id=\"\" align=\"aligncenter\" width=\"487\"]<img src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/3675\/2018\/09\/27165233\/CNX_Precalc_Figure_08_02_0112.jpg\" alt=\"A triangle formed by sides Rush Street, N. Wabash Ave, and E. Pearson Street with lengths 62.4, 43.5, and 34.1, respectively. \" width=\"487\" height=\"520\" \/> <b>Figure 10<\/b>[\/caption]\r\n\r\n[reveal-answer q=\"63725\"]Show Solution[\/reveal-answer]\r\n[hidden-answer a=\"63725\"]\r\n\r\nFind the measurement for [latex]s[\/latex], which is one-half of the perimeter.\r\n<p style=\"text-align: center;\">[latex]\\begin{align}s&amp;=\\frac{\\left(62.4+43.5+34.1\\right)}{2} \\\\ s&amp;=70\\text{m} \\end{align}[\/latex]<\/p>\r\nApply Heron\u2019s formula.\r\n<p style=\"text-align: center;\">[latex]\\begin{align}\\text{Area}&amp;=\\sqrt{70\\left(70 - 62.4\\right)\\left(70 - 43.5\\right)\\left(70 - 34.1\\right)} \\\\ \\text{Area}&amp;=\\sqrt{506,118.2} \\\\ \\text{Area}&amp;\\approx 711.4 \\end{align}[\/latex]<\/p>\r\nThe developer has about 711.4 square meters.\r\n\r\n[\/hidden-answer]\r\n\r\n<\/div>\r\n<div class=\"bcc-box bcc-success\">\r\n<h3>Try It<\/h3>\r\nFind the area of a triangle given [latex]a=4.38\\text{ft},b=3.79\\text{ft,}[\/latex] and [latex]c=5.22\\text{ft}\\text{.}[\/latex]\r\n\r\n[reveal-answer q=\"942985\"]Show Solution[\/reveal-answer]\r\n[hidden-answer a=\"942985\"]\r\n\r\nabout 8.15 square feet\r\n\r\n[\/hidden-answer]\r\n\r\n<\/div>\r\n<div class=\"textbox key-takeaways\">\r\n<h3>Try It<\/h3>\r\n[ohm_question hide_question_numbers=1 height=\"470\"]8473[\/ohm_question]\r\n\r\n<\/div>\r\n<h2>Key Equations<\/h2>\r\n<table id=\"eip-id1956425\" summary=\"..\">\r\n<tbody>\r\n<tr>\r\n<td>Law of Cosines<\/td>\r\n<td>\r\n<p style=\"text-align: left;\">[latex]{a}^{2}={b}^{2}+{c}^{2}-2bc\\cos \\alpha[\/latex]<\/p>\r\n<p style=\"text-align: left;\">[latex]{b}^{2}={a}^{2}+{c}^{2}-2ac\\cos \\beta[\/latex]<\/p>\r\n<p style=\"text-align: left;\">[latex]{c}^{2}={a}^{2}+{b}^{2}-2ab\\cos \\gamma [\/latex]<\/p>\r\n<\/td>\r\n<\/tr>\r\n<tr>\r\n<td>Heron\u2019s formula<\/td>\r\n<td>[latex]\\text{Area}=\\sqrt{s\\left(s-a\\right)\\left(s-b\\right)\\left(s-c\\right)}[\/latex] where [latex]s=\\frac{\\left(a+b+c\\right)}{2}[\/latex]<\/td>\r\n<\/tr>\r\n<\/tbody>\r\n<\/table>\r\n<h2>Key Concepts<\/h2>\r\n<ul>\r\n \t<li>The Law of Cosines defines the relationship among angle measurements and lengths of sides in oblique triangles.<\/li>\r\n \t<li>The Generalized Pythagorean Theorem is the Law of Cosines for two cases of oblique triangles: SAS and SSS. Dropping an imaginary perpendicular splits the oblique triangle into two right triangles or forms one right triangle, which allows sides to be related and measurements to be calculated.<\/li>\r\n \t<li>The Law of Cosines is useful for many types of applied problems. The first step in solving such problems is generally to draw a sketch of the problem presented. If the information given fits one of the three models (the three equations), then apply the Law of Cosines to find a solution.<\/li>\r\n \t<li>Heron\u2019s formula allows the calculation of area in oblique triangles. All three sides must be known to apply Heron\u2019s formula.<\/li>\r\n<\/ul>\r\n<div>\r\n<dl id=\"fs-id1165133184256\" class=\"definition\">\r\n \t<dd id=\"fs-id1165133184261\"><\/dd>\r\n \t<dd>\r\n<dl id=\"fs-id1165133184256\" class=\"definition\">\r\n \t<dd>\r\n<h2>Glossary<\/h2>\r\n<dl id=\"fs-id1165135690077\" class=\"definition\">\r\n \t<dt>Law of Cosines<\/dt>\r\n \t<dd id=\"fs-id1165135690083\">states that the square of any side of a triangle is equal to the sum of the squares of the other two sides minus twice the product of the other two sides and the cosine of the included angle<\/dd>\r\n<\/dl>\r\n<dl id=\"fs-id1165133184256\" class=\"definition\">\r\n \t<dt>Generalized Pythagorean Theorem<\/dt>\r\n \t<dd id=\"fs-id1165133184261\">an extension of the Law of Cosines; relates the sides of an oblique triangle and is used for SAS and SSS triangles<\/dd>\r\n<\/dl>\r\n<\/dd>\r\n<\/dl>\r\n<dl id=\"fs-id1165133184256\" class=\"definition\">\r\n \t<dd id=\"fs-id1165133184261\"><\/dd>\r\n<\/dl>\r\n<\/dd>\r\n<\/dl>\r\n<\/div>","rendered":"<div class=\"bcc-box bcc-highlight\">\n<h3>Learning Outcomes<\/h3>\n<ul>\n<li>Use the Law of Cosines to solve oblique triangles.<\/li>\n<li>Solve applied problems using the Law of Cosines.<\/li>\n<li>Use Heron\u2019s formula to \ufb01nd the area of a triangle.<\/li>\n<\/ul>\n<\/div>\n<p>Suppose a boat leaves port, travels 10 miles, turns 20 degrees, and travels another 8 miles as shown in Figure 1.\u00a0How far from port is the boat?<\/p>\n<div style=\"width: 497px\" class=\"wp-caption aligncenter\"><img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/3675\/2018\/09\/27165212\/CNX_Precalc_Figure_08_02_0012.jpg\" alt=\"A triangle whose vertices are the boat, the port, and the turning point of the boat. The side between the port and the turning point is 10 mi, and the side between the turning point and the boat is 8 miles. The side between the port and the turning point is extended in a straight dotted line. The angle between the dotted line and the 8 mile side is 20 degrees.\" width=\"487\" height=\"517\" \/><\/p>\n<p class=\"wp-caption-text\"><b>Figure 1<\/b><\/p>\n<\/div>\n<p>Unfortunately, while the Law of Sines enables us to address many non-right triangle cases, it does not help us with triangles where the known angle is between two known sides, a <strong>SAS (side-angle-side) triangle<\/strong>, or when all three sides are known, but no angles are known, a <strong>SSS (side-side-side) triangle<\/strong>. In this section, we will investigate another tool for solving oblique triangles described by these last two cases.<\/p>\n<h2>Using the Law of Cosines to Solve Oblique Triangles<\/h2>\n<p>The tool we need to solve the problem of the boat\u2019s distance from the port is the <strong>Law of Cosines<\/strong>, which defines the relationship among angle measurements and side lengths in oblique triangles. Three formulas make up the Law of Cosines. At first glance, the formulas may appear complicated because they include many variables. However, once the pattern is understood, the Law of Cosines is easier to work with than most formulas at this mathematical level.<\/p>\n<p>Understanding how the Law of Cosines is derived will be helpful in using the formulas. The derivation begins with the <strong>Generalized Pythagorean Theorem<\/strong>, which is an extension of the <strong>Pythagorean Theorem<\/strong> to non-right triangles. Here is how it works: An arbitrary non-right triangle [latex]ABC[\/latex] is placed in the coordinate plane with vertex [latex]A[\/latex] at the origin, side [latex]c[\/latex] drawn along the <em>x<\/em>-axis, and vertex [latex]C[\/latex] located at some point [latex]\\left(x,y\\right)[\/latex] in the plane, as illustrated in Figure 2. Generally, triangles exist anywhere in the plane, but for this explanation we will place the triangle as noted.<\/p>\n<div style=\"width: 497px\" class=\"wp-caption aligncenter\"><img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/3675\/2018\/09\/27165215\/CNX_Precalc_Figure_08_02_0022.jpg\" alt=\"A triangle A B C plotted in quadrant 1 of the x,y plane. Angle A is theta degrees with opposite side a, angles B and C, with opposite sides b and c respectively, are unknown. Vertex A is located at the origin (0,0), vertex B is located at some point (x-c, 0) along the x-axis, and point C is located at some point in quadrant 1 at the point (b times the cos of theta, b times the sin of theta).\" width=\"487\" height=\"266\" \/><\/p>\n<p class=\"wp-caption-text\"><b>Figure 2<\/b><\/p>\n<\/div>\n<p>We can drop a perpendicular from [latex]C[\/latex] to the <em>x-<\/em>axis (this is the altitude or height). Recalling the basic <strong>trigonometric identities<\/strong>, we know that<\/p>\n<div style=\"text-align: center;\">[latex]\\cos \\theta =\\frac{x\\text{(adjacent)}}{b\\text{(hypotenuse)}}\\text{ and }\\sin \\theta =\\frac{y\\text{(opposite)}}{b\\text{(hypotenuse)}}[\/latex]<\/div>\n<p>In terms of [latex]\\theta ,\\text{ }x=b\\cos \\theta[\/latex] and [latex]y=b\\sin \\theta .\\text{ }[\/latex] The [latex]\\left(x,y\\right)[\/latex] point located at [latex]C[\/latex] has coordinates [latex]\\left(b\\cos \\theta ,b\\sin \\theta \\right)[\/latex]. Using the side [latex]\\left(x-c\\right)[\/latex] as one leg of a right triangle and [latex]y[\/latex] as the second leg, we can find the length of hypotenuse [latex]a[\/latex] using the Pythagorean Theorem. Thus,<\/p>\n<div style=\"text-align: center;\">[latex]\\begin{align} {a}^{2}&={\\left(x-c\\right)}^{2}+{y}^{2} \\\\ &={\\left(b\\cos \\theta -c\\right)}^{2}+{\\left(b\\sin \\theta \\right)}^{2} && \\text{Substitute }\\left(b\\cos \\theta \\right)\\text{ for}x\\text{and }\\left(b\\sin \\theta \\right)\\text{for }y. \\\\ &=\\left({b}^{2}{\\cos }^{2}\\theta -2bc\\cos \\theta +{c}^{2}\\right)+{b}^{2}{\\sin }^{2}\\theta && \\text{Expand the perfect square}. \\\\ &={b}^{2}{\\cos }^{2}\\theta +{b}^{2}{\\sin }^{2}\\theta +{c}^{2}-2bc\\cos \\theta && \\text{Group terms noting that }{\\cos }^{2}\\theta +{\\sin }^{2}\\theta =1. \\\\ &={b}^{2}\\left({\\cos }^{2}\\theta +{\\sin }^{2}\\theta \\right)+{c}^{2}-2bc\\cos \\theta && \\text{Factor out }{b}^{2}. \\\\ {a}^{2}&={b}^{2}+{c}^{2}-2bc\\cos \\theta &&{\\cos }^{2}\\theta +{\\sin }^{2}\\theta = 1 \\end{align}[\/latex]<\/div>\n<p>The formula derived is one of the three equations of the Law of Cosines. The other equations are found in a similar fashion.<\/p>\n<p>Keep in mind that it is always helpful to sketch the triangle when solving for angles or sides. In a real-world scenario, try to draw a diagram of the situation. As more information emerges, the diagram may have to be altered. Make those alterations to the diagram and, in the end, the problem will be easier to solve.<\/p>\n<div class=\"textbox\">\n<h3>A General Note: Law of Cosines<\/h3>\n<p>The <strong>Law of Cosines<\/strong> states that the square of any side of a triangle is equal to the sum of the squares of the other two sides minus twice the product of the other two sides and the cosine of the included angle. For triangles labeled as in Figure 3, with angles [latex]\\alpha ,\\beta[\/latex], and [latex]\\gamma[\/latex], and opposite corresponding sides [latex]a,b[\/latex], and [latex]c[\/latex], respectively, the Law of Cosines is given as three equations.<\/p>\n<p style=\"text-align: center;\">[latex]{a}^{2}={b}^{2}+{c}^{2}-2bc\\cos \\alpha[\/latex]<\/p>\n<p style=\"text-align: center;\">[latex]{b}^{2}={a}^{2}+{c}^{2}-2ac\\cos \\beta[\/latex]<\/p>\n<p style=\"text-align: center;\">[latex]{c}^{2}={a}^{2}+{b}^{2}-2ab\\cos \\gamma[\/latex]<\/p>\n<div style=\"width: 497px\" class=\"wp-caption aligncenter\"><img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/3675\/2018\/09\/27165217\/CNX_Precalc_Figure_08_02_003n2.jpg\" alt=\"A triangle with standard labels: angles alpha, beta, and gamma with opposite sides a, b, and c respectively.\" width=\"487\" height=\"239\" \/><\/p>\n<p class=\"wp-caption-text\"><b>Figure 3<\/b><\/p>\n<\/div>\n<p>To solve for a missing side measurement, the corresponding opposite angle measure is needed.<\/p>\n<p>When solving for an angle, the corresponding opposite side measure is needed. We can use another version of the Law of Cosines to solve for an angle.<\/p>\n<p style=\"text-align: center;\">[latex]\\cos \\alpha =\\frac{{b}^{2}+{c}^{2}-{a}^{2}}{2bc}[\/latex]<\/p>\n<p style=\"text-align: center;\">[latex]\\cos \\beta =\\frac{{a}^{2}+{c}^{2}-{b}^{2}}{2ac}[\/latex]<\/p>\n<p style=\"text-align: center;\">[latex]\\cos\\gamma =\\frac{{a}^{2}+{b}^{2}-{c}^{2}}{2ab}[\/latex]<\/p>\n<\/div>\n<div class=\"textbox\">\n<h3>How To:\u00a0Given two sides and the angle between them (SAS), find the measures of the remaining side and angles of a triangle.<\/h3>\n<ol id=\"fs-id1165132949849\">\n<li>Sketch the triangle. Identify the measures of the known sides and angles. Use variables to represent the measures of the unknown sides and angles.<\/li>\n<li>Apply the Law of Cosines to find the length of the unknown side or angle.<\/li>\n<li>Apply the <strong>Law of Sines<\/strong> or Cosines to find the measure of a second angle.<\/li>\n<li>Compute the measure of the remaining angle.<\/li>\n<\/ol>\n<\/div>\n<div class=\"textbox shaded\">\n<h3>Example 1: Finding the Unknown Side and Angles of a SAS Triangle<\/h3>\n<p>Find the unknown side and angles of the triangle in Figure 4.<\/p>\n<div style=\"width: 497px\" class=\"wp-caption aligncenter\"><img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/3675\/2018\/09\/27165219\/CNX_Precalc_Figure_08_02_0042.jpg\" alt=\"A triangle with standard labels. Side a = 10, side c = 12, and angle beta = 30 degrees.\" width=\"487\" height=\"189\" \/><\/p>\n<p class=\"wp-caption-text\"><b>Figure 4<\/b><\/p>\n<\/div>\n<div class=\"qa-wrapper\" style=\"display: block\"><span class=\"show-answer collapsed\" style=\"cursor: pointer\" data-target=\"q359338\">Show Solution<\/span><\/p>\n<div id=\"q359338\" class=\"hidden-answer\" style=\"display: none\">\n<p>First, make note of what is given: two sides and the angle between them. This arrangement is classified as SAS and supplies the data needed to apply the Law of Cosines.<\/p>\n<p>Each one of the three laws of cosines begins with the square of an unknown side opposite a known angle. For this example, the first side to solve for is side [latex]b[\/latex], as we know the measurement of the opposite angle [latex]\\beta[\/latex].<\/p>\n<p style=\"text-align: center;\">[latex]\\begin{align}&{b}^{2}={a}^{2}+{c}^{2}-2ac\\cos \\beta \\\\ &{b}^{2}={10}^{2}+{12}^{2}-2\\left(10\\right)\\left(12\\right)\\cos \\left({30}^{\\circ }\\right) && \\text{Substitute the measurements for the known quantities}. \\\\ &{b}^{2}=100+144 - 240\\left(\\frac{\\sqrt{3}}{2}\\right)&& \\text{Evaluate the cosine and begin to simplify}. \\\\ &{b}^{2}=244 - 120\\sqrt{3} \\\\ &b=\\sqrt{244 - 120\\sqrt{3}}&& \\text{Use the square root property}. \\\\ &b\\approx 6.013 \\end{align}[\/latex]<\/p>\n<p>Because we are solving for a length, we use only the positive square root. Now that we know the length [latex]b[\/latex], we can use the Law of Sines to fill in the remaining angles of the triangle. Solving for angle [latex]\\alpha[\/latex], we have<\/p>\n<p style=\"text-align: center;\">[latex]\\begin{align}&\\frac{\\sin \\alpha }{a}=\\frac{\\sin \\beta }{b} \\\\ &\\frac{\\sin \\alpha }{10}=\\frac{\\sin \\left(30^\\circ \\right)}{6.013} \\\\ &\\sin \\alpha =\\frac{10\\sin \\left(30^\\circ \\right)}{6.013}&& \\text{Multiply both sides of the equation by 10}. \\\\ &\\alpha ={\\sin }^{-1}\\left(\\frac{10\\sin \\left(30^\\circ \\right)}{6.013}\\right)&& \\text{Find the inverse sine of }\\frac{10\\sin \\left(30^\\circ \\right)}{6.013}. \\\\ &\\alpha \\approx 56.3^\\circ \\end{align}[\/latex]<\/p>\n<p>The other possibility for [latex]\\alpha[\/latex] would be [latex]\\alpha =180^\\circ -56.3^\\circ \\approx 123.7^\\circ[\/latex]. In the original diagram, [latex]\\alpha[\/latex] is adjacent to the longest side, so [latex]\\alpha[\/latex] is an acute angle and, therefore, [latex]123.7^\\circ[\/latex] does not make sense. Notice that if we choose to apply the <strong>Law of Cosines<\/strong>, we arrive at a unique answer. We do not have to consider the other possibilities, as cosine is unique for angles between [latex]0^\\circ[\/latex] and [latex]180^\\circ[\/latex]. Proceeding with [latex]\\alpha \\approx 56.3^\\circ[\/latex], we can then find the third angle of the triangle.<\/p>\n<p style=\"text-align: center;\">[latex]\\gamma =180^\\circ -30^\\circ -56.3^\\circ \\approx 93.7^\\circ[\/latex]<\/p>\n<p>The complete set of angles and sides is<\/p>\n<p style=\"text-align: center;\">[latex]\\begin{align}&\\alpha \\approx 56.3^\\circ && a=10\\\\ &\\beta =30^\\circ && b\\approx 6.013\\\\ &\\gamma \\approx 93.7^\\circ && c=12 \\end{align}[\/latex]<\/p>\n<\/div>\n<\/div>\n<\/div>\n<div class=\"bcc-box bcc-success\">\n<h3>Try It<\/h3>\n<p>Find the missing side and angles of the given triangle: [latex]\\alpha =30^\\circ ,b=12,c=24[\/latex].<\/p>\n<div class=\"qa-wrapper\" style=\"display: block\"><span class=\"show-answer collapsed\" style=\"cursor: pointer\" data-target=\"q885435\">Show Solution<\/span><\/p>\n<div id=\"q885435\" class=\"hidden-answer\" style=\"display: none\">\n<p>[latex]a\\approx 14.9,\\beta \\approx 23.8^\\circ ,\\gamma \\approx 126.2^\\circ[\/latex].<\/p>\n<\/div>\n<\/div>\n<\/div>\n<div class=\"textbox key-takeaways\">\n<h3>Try It<\/h3>\n<p><iframe loading=\"lazy\" id=\"ohm174837\" class=\"resizable\" src=\"https:\/\/ohm.lumenlearning.com\/multiembedq.php?id=174837&theme=oea&iframe_resize_id=ohm174837\" width=\"100%\" height=\"270\"><\/iframe><\/p>\n<\/div>\n<div class=\"textbox shaded\">\n<h3>Example 2: Solving for an Angle of a SSS Triangle<\/h3>\n<p>Find the angle [latex]\\alpha[\/latex] for the given triangle if side [latex]a=20[\/latex], side [latex]b=25[\/latex], and side [latex]c=18[\/latex].<\/p>\n<div class=\"qa-wrapper\" style=\"display: block\"><span class=\"show-answer collapsed\" style=\"cursor: pointer\" data-target=\"q211238\">Show Solution<\/span><\/p>\n<div id=\"q211238\" class=\"hidden-answer\" style=\"display: none\">\n<p>For this example, we have no angles. We can solve for any angle using the Law of Cosines. To solve for angle [latex]\\alpha[\/latex], we have<\/p>\n<p style=\"text-align: center;\">[latex]\\begin{align} &{a}^{2}={b}^{2}+{c}^{2}-2bc\\cos \\alpha \\\\ &{20}^{2}={25}^{2}+{18}^{2}-2\\left(25\\right)\\left(18\\right)\\cos \\alpha&& \\text{Substitute the appropriate measurements}. \\\\ &400=625+324 - 900\\cos \\alpha&& \\text{Simplify in each step}. \\\\ &400=949 - 900\\cos \\alpha \\\\ &-549=-900\\cos \\alpha&& \\text{Isolate cos }\\alpha . \\\\ &\\frac{-549}{-900}=\\cos \\alpha \\\\ &0.61\\approx \\cos \\alpha \\\\ &{\\cos }^{-1}\\left(0.61\\right)\\approx \\alpha&& \\text{Find the inverse cosine}. \\\\ &\\alpha \\approx 52.4^\\circ \\end{align}[\/latex]<\/p>\n<p>See Figure 5.<\/p>\n<div style=\"width: 497px\" class=\"wp-caption aligncenter\"><img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/3675\/2018\/09\/27165221\/CNX_Precalc_Figure_08_02_0052.jpg\" alt=\"A triangle with standard labels. Side b =25, side a = 20, side c = 18, and angle alpha = 52.4 degrees.\" width=\"487\" height=\"266\" \/><\/p>\n<p class=\"wp-caption-text\"><b>Figure 5<\/b><\/p>\n<\/div>\n<h4>Analysis of the Solution<\/h4>\n<p>Because the inverse cosine can return any angle between 0 and 180 degrees, there will not be any ambiguous cases using this method.<\/p>\n<\/div>\n<\/div>\n<\/div>\n<div class=\"bcc-box bcc-success\">\n<h3>Try It<\/h3>\n<p>Given [latex]a=5,b=7[\/latex], and [latex]c=10[\/latex], find the missing angles.<\/p>\n<div class=\"qa-wrapper\" style=\"display: block\"><span class=\"show-answer collapsed\" style=\"cursor: pointer\" data-target=\"q488277\">Show Solution<\/span><\/p>\n<div id=\"q488277\" class=\"hidden-answer\" style=\"display: none\">\n<p>[latex]\\alpha \\approx 27.7^\\circ ,\\beta \\approx 40.5^\\circ ,\\gamma \\approx 111.8^\\circ[\/latex]<\/p>\n<\/div>\n<\/div>\n<\/div>\n<div class=\"textbox key-takeaways\">\n<h3>Try It<\/h3>\n<p><iframe loading=\"lazy\" id=\"ohm173789\" class=\"resizable\" src=\"https:\/\/ohm.lumenlearning.com\/multiembedq.php?id=173789&theme=oea&iframe_resize_id=ohm173789\" width=\"100%\" height=\"350\"><\/iframe><\/p>\n<\/div>\n<h2>Solving Applied Problems Using the Law of Cosines<\/h2>\n<p>Just as the Law of Sines provided the appropriate equations to solve a number of applications, the Law of Cosines is applicable to situations in which the given data fits the cosine models. We may see these in the fields of navigation, surveying, astronomy, and geometry, just to name a few.<\/p>\n<div class=\"textbox shaded\">\n<h3>Example 3: Using the Law of Cosines to Solve a Communication Problem<\/h3>\n<p>On many cell phones with GPS, an approximate location can be given before the GPS signal is received. This is accomplished through a process called triangulation, which works by using the distances from two known points. Suppose there are two cell phone towers within range of a cell phone. The two towers are located 6000 feet apart along a straight highway, running east to west, and the cell phone is north of the highway. Based on the signal delay, it can be determined that the signal is 5050 feet from the first tower and 2420 feet from the second tower. Determine the position of the cell phone north and east of the first tower, and determine how far it is from the highway.<\/p>\n<div class=\"qa-wrapper\" style=\"display: block\"><span class=\"show-answer collapsed\" style=\"cursor: pointer\" data-target=\"q960347\">Show Solution<\/span><\/p>\n<div id=\"q960347\" class=\"hidden-answer\" style=\"display: none\">\n<p>For simplicity, we start by drawing a diagram similar to Figure 6\u00a0and labeling our given information.<\/p>\n<div style=\"width: 497px\" class=\"wp-caption aligncenter\"><img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/3675\/2018\/09\/27165224\/CNX_Precalc_Figure_08_02_0062.jpg\" alt=\"A triangle formed between the two cell phone towers located on am east to west highway and the cellphone between and north of them. The side between the two towers is 6000 feet, the side between the left tower and the phone is 5050 feet, and the side between the right tower and the phone is 2420 feet. The angle between the 5050 and 6000 feet sides is labeled theta.\" width=\"487\" height=\"199\" \/><\/p>\n<p class=\"wp-caption-text\"><b>Figure 6<\/b><\/p>\n<\/div>\n<p>Using the Law of Cosines, we can solve for the angle [latex]\\theta[\/latex]. Remember that the Law of Cosines uses the square of one side to find the cosine of the opposite angle. For this example, let [latex]a=2420,b=5050[\/latex], and [latex]c=6000[\/latex]. Thus, [latex]\\theta[\/latex] corresponds to the opposite side [latex]a=2420[\/latex].<\/p>\n<p style=\"text-align: center;\">[latex]\\begin{gathered}{a}^{2}={b}^{2}+{c}^{2}-2bc\\cos \\theta \\\\ {\\left(2420\\right)}^{2}={\\left(5050\\right)}^{2}+{\\left(6000\\right)}^{2}-2\\left(5050\\right)\\left(6000\\right)\\cos \\theta \\\\ {\\left(2420\\right)}^{2}-{\\left(5050\\right)}^{2}-{\\left(6000\\right)}^{2}=-2\\left(5050\\right)\\left(6000\\right)\\cos \\theta \\\\ \\frac{{\\left(2420\\right)}^{2}-{\\left(5050\\right)}^{2}-{\\left(6000\\right)}^{2}}{-2\\left(5050\\right)\\left(6000\\right)}=\\cos \\theta \\\\ \\cos \\theta \\approx 0.9183 \\\\ \\theta \\approx {\\cos }^{-1}\\left(0.9183\\right) \\\\ \\theta \\approx 23.3^\\circ \\end{gathered}[\/latex]<\/p>\n<p>To answer the questions about the phone\u2019s position north and east of the tower, and the distance to the highway, drop a perpendicular from the position of the cell phone, as in Figure 7.\u00a0This forms two right triangles, although we only need the right triangle that includes the first tower for this problem.<\/p>\n<div style=\"width: 497px\" class=\"wp-caption aligncenter\"><img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/3675\/2018\/09\/27165226\/CNX_Precalc_Figure_08_02_0072.jpg\" alt=\"The triangle between the phone, the left tower, and a point between the phone and the highway between the towers. The side between the phone and the highway is perpendicular to the highway and is y feet. The highway side is x feet. The angle at the tower, previously labeled theta, is 23.3 degrees.\" width=\"487\" height=\"177\" \/><\/p>\n<p class=\"wp-caption-text\"><b>Figure 7<\/b><\/p>\n<\/div>\n<p>Using the angle [latex]\\theta =23.3^\\circ[\/latex] and the basic trigonometric identities, we can find the solutions. Thus<\/p>\n<p style=\"text-align: center;\">[latex]\\begin{gathered} \\cos \\left(23.3^\\circ \\right)=\\frac{x}{5050} \\\\ x=5050\\cos \\left(23.3^\\circ \\right) \\\\ x\\approx 4638.15\\text{feet} \\\\ \\sin \\left(23.3^\\circ \\right)=\\frac{y}{5050} \\\\ y=5050\\sin \\left(23.3^\\circ \\right) \\\\ y\\approx 1997.5\\text{feet} \\end{gathered}[\/latex]<\/p>\n<p>The cell phone is approximately 4638 feet east and 1998 feet north of the first tower, and 1998 feet from the highway.<\/p>\n<\/div>\n<\/div>\n<\/div>\n<div class=\"textbox shaded\">\n<h3>Example 4: Calculating Distance Traveled Using a SAS Triangle<\/h3>\n<p>Returning to our problem at the beginning of this section, suppose a boat leaves port, travels 10 miles, turns 20 degrees, and travels another 8 miles. How far from port is the boat? The diagram is repeated here in Figure 8.<\/p>\n<div style=\"width: 497px\" class=\"wp-caption aligncenter\"><img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/3675\/2018\/09\/27165228\/CNX_Precalc_Figure_08_02_0092.jpg\" alt=\"A triangle whose vertices are the boat, the port, and the turning point of the boat. The side between the port and the turning point is 10 mi, and the side between the turning point and the boat is 8 miles. The side between the port and the turning point is extended in a straight dotted line. The angle between the dotted line and the 8 mile side is 20 degrees.\" width=\"487\" height=\"517\" \/><\/p>\n<p class=\"wp-caption-text\"><b>Figure 8<\/b><\/p>\n<\/div>\n<div class=\"qa-wrapper\" style=\"display: block\"><span class=\"show-answer collapsed\" style=\"cursor: pointer\" data-target=\"q569516\">Show Solution<\/span><\/p>\n<div id=\"q569516\" class=\"hidden-answer\" style=\"display: none\">\n<p>The boat turned 20 degrees, so the obtuse angle of the non-right triangle is the supplemental angle, [latex]180^\\circ -20^\\circ =160^\\circ[\/latex]. With this, we can utilize the Law of Cosines to find the missing side of the obtuse triangle\u2014the distance of the boat to the port.<\/p>\n<p style=\"text-align: center;\">[latex]\\begin{align}&{x}^{2}={8}^{2}+{10}^{2}-2\\left(8\\right)\\left(10\\right)\\cos \\left(160^\\circ \\right) \\\\ &{x}^{2}=314.35 \\\\ &x=\\sqrt{314.35} \\\\ &x\\approx 17.7\\text{miles} \\end{align}[\/latex]<\/p>\n<p>The boat is about 17.7 miles from port.<\/p>\n<\/div>\n<\/div>\n<\/div>\n<h2>Using Heron&#8217;s Formula to Find the Area of a Triangle<\/h2>\n<p>We already learned how to find the area of an oblique triangle when we know two sides and an angle. We also know the formula to find the area of a triangle using the base and the height. When we know the three sides, however, we can use <strong>Heron\u2019s formula<\/strong> instead of finding the height. <strong>Heron of Alexandria<\/strong> was a geometer who lived during the first century A.D. He discovered a formula for finding the area of oblique triangles when three sides are known.<\/p>\n<div class=\"textbox\">\n<h3>A General Note: Heron\u2019s Formula<\/h3>\n<p>Heron\u2019s formula finds the area of oblique triangles in which sides [latex]a,b[\/latex], and [latex]c[\/latex] are known.<\/p>\n<p style=\"text-align: center;\">[latex]\\text{Area}=\\sqrt{s\\left(s-a\\right)\\left(s-b\\right)\\left(s-c\\right)}[\/latex]<\/p>\n<p>where [latex]s=\\frac{\\left(a+b+c\\right)}{2}[\/latex] is one half of the perimeter of the triangle, sometimes called the semi-perimeter.<\/p>\n<\/div>\n<div class=\"textbox shaded\">\n<h3>Example 5: Using Heron\u2019s Formula to Find the Area of a Given Triangle<\/h3>\n<p>Find the area of the triangle in Figure 9\u00a0using Heron\u2019s formula.<\/p>\n<div style=\"width: 497px\" class=\"wp-caption aligncenter\"><img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/3675\/2018\/09\/27165230\/CNX_Precalc_Figure_08_02_0102.jpg\" alt=\"A triangle with angles A, B, and C and opposite sides a, b, and c, respectively. Side a = 10, side b - 15, and side c = 7.\" width=\"487\" height=\"134\" \/><\/p>\n<p class=\"wp-caption-text\"><b>Figure 9<\/b><\/p>\n<\/div>\n<div class=\"qa-wrapper\" style=\"display: block\"><span class=\"show-answer collapsed\" style=\"cursor: pointer\" data-target=\"q256710\">Show Solution<\/span><\/p>\n<div id=\"q256710\" class=\"hidden-answer\" style=\"display: none\">\n<p>First, we calculate [latex]s[\/latex].<\/p>\n<p style=\"text-align: center;\">[latex]\\begin{align} s&=\\frac{\\left(a+b+c\\right)}{2} \\\\ s&=\\frac{\\left(10+15+7\\right)}{2}=16 \\end{align}[\/latex]<\/p>\n<p>Then we apply the formula.<\/p>\n<p style=\"text-align: center;\">[latex]\\begin{align} \\text{Area}&=\\sqrt{s\\left(s-a\\right)\\left(s-b\\right)\\left(s-c\\right)} \\\\ \\text{Area}&=\\sqrt{16\\left(16 - 10\\right)\\left(16 - 15\\right)\\left(16 - 7\\right)} \\\\ \\text{Area}&\\approx 29.4 \\end{align}[\/latex]<\/p>\n<p>The area is approximately 29.4 square units.<\/p>\n<\/div>\n<\/div>\n<\/div>\n<div class=\"bcc-box bcc-success\">\n<h3>Try It<\/h3>\n<p>Use Heron\u2019s formula to find the area of a triangle with sides of lengths [latex]a=29.7\\text{ft},b=42.3\\text{ft}[\/latex], and [latex]c=38.4\\text{ft}[\/latex].<\/p>\n<div class=\"qa-wrapper\" style=\"display: block\"><span class=\"show-answer collapsed\" style=\"cursor: pointer\" data-target=\"q159200\">Show Solution<\/span><\/p>\n<div id=\"q159200\" class=\"hidden-answer\" style=\"display: none\">\n<p>Area = 552 square feet<\/p>\n<\/div>\n<\/div>\n<\/div>\n<div class=\"textbox key-takeaways\">\n<h3>Try It<\/h3>\n<p><iframe loading=\"lazy\" id=\"ohm149312\" class=\"resizable\" src=\"https:\/\/ohm.lumenlearning.com\/multiembedq.php?id=149312&theme=oea&iframe_resize_id=ohm149312\" width=\"100%\" height=\"350\"><\/iframe><\/p>\n<\/div>\n<div class=\"textbox shaded\">\n<h3>Example 6: Applying Heron\u2019s Formula to a Real-World Problem<\/h3>\n<p>A Chicago city developer wants to construct a building consisting of artist\u2019s lofts on a triangular lot bordered by Rush Street, Wabash Avenue, and Pearson Street. The frontage along Rush Street is approximately 62.4 meters, along Wabash Avenue it is approximately 43.5 meters, and along Pearson Street it is approximately 34.1 meters. How many square meters are available to the developer? See Figure 10\u00a0for a view of the city property.<\/p>\n<div style=\"width: 497px\" class=\"wp-caption aligncenter\"><img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/3675\/2018\/09\/27165233\/CNX_Precalc_Figure_08_02_0112.jpg\" alt=\"A triangle formed by sides Rush Street, N. Wabash Ave, and E. Pearson Street with lengths 62.4, 43.5, and 34.1, respectively.\" width=\"487\" height=\"520\" \/><\/p>\n<p class=\"wp-caption-text\"><b>Figure 10<\/b><\/p>\n<\/div>\n<div class=\"qa-wrapper\" style=\"display: block\"><span class=\"show-answer collapsed\" style=\"cursor: pointer\" data-target=\"q63725\">Show Solution<\/span><\/p>\n<div id=\"q63725\" class=\"hidden-answer\" style=\"display: none\">\n<p>Find the measurement for [latex]s[\/latex], which is one-half of the perimeter.<\/p>\n<p style=\"text-align: center;\">[latex]\\begin{align}s&=\\frac{\\left(62.4+43.5+34.1\\right)}{2} \\\\ s&=70\\text{m} \\end{align}[\/latex]<\/p>\n<p>Apply Heron\u2019s formula.<\/p>\n<p style=\"text-align: center;\">[latex]\\begin{align}\\text{Area}&=\\sqrt{70\\left(70 - 62.4\\right)\\left(70 - 43.5\\right)\\left(70 - 34.1\\right)} \\\\ \\text{Area}&=\\sqrt{506,118.2} \\\\ \\text{Area}&\\approx 711.4 \\end{align}[\/latex]<\/p>\n<p>The developer has about 711.4 square meters.<\/p>\n<\/div>\n<\/div>\n<\/div>\n<div class=\"bcc-box bcc-success\">\n<h3>Try It<\/h3>\n<p>Find the area of a triangle given [latex]a=4.38\\text{ft},b=3.79\\text{ft,}[\/latex] and [latex]c=5.22\\text{ft}\\text{.}[\/latex]<\/p>\n<div class=\"qa-wrapper\" style=\"display: block\"><span class=\"show-answer collapsed\" style=\"cursor: pointer\" data-target=\"q942985\">Show Solution<\/span><\/p>\n<div id=\"q942985\" class=\"hidden-answer\" style=\"display: none\">\n<p>about 8.15 square feet<\/p>\n<\/div>\n<\/div>\n<\/div>\n<div class=\"textbox key-takeaways\">\n<h3>Try It<\/h3>\n<p><iframe loading=\"lazy\" id=\"ohm8473\" class=\"resizable\" src=\"https:\/\/ohm.lumenlearning.com\/multiembedq.php?id=8473&theme=oea&iframe_resize_id=ohm8473\" width=\"100%\" height=\"470\"><\/iframe><\/p>\n<\/div>\n<h2>Key Equations<\/h2>\n<table id=\"eip-id1956425\" summary=\"..\">\n<tbody>\n<tr>\n<td>Law of Cosines<\/td>\n<td>\n<p style=\"text-align: left;\">[latex]{a}^{2}={b}^{2}+{c}^{2}-2bc\\cos \\alpha[\/latex]<\/p>\n<p style=\"text-align: left;\">[latex]{b}^{2}={a}^{2}+{c}^{2}-2ac\\cos \\beta[\/latex]<\/p>\n<p style=\"text-align: left;\">[latex]{c}^{2}={a}^{2}+{b}^{2}-2ab\\cos \\gamma[\/latex]<\/p>\n<\/td>\n<\/tr>\n<tr>\n<td>Heron\u2019s formula<\/td>\n<td>[latex]\\text{Area}=\\sqrt{s\\left(s-a\\right)\\left(s-b\\right)\\left(s-c\\right)}[\/latex] where [latex]s=\\frac{\\left(a+b+c\\right)}{2}[\/latex]<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<h2>Key Concepts<\/h2>\n<ul>\n<li>The Law of Cosines defines the relationship among angle measurements and lengths of sides in oblique triangles.<\/li>\n<li>The Generalized Pythagorean Theorem is the Law of Cosines for two cases of oblique triangles: SAS and SSS. Dropping an imaginary perpendicular splits the oblique triangle into two right triangles or forms one right triangle, which allows sides to be related and measurements to be calculated.<\/li>\n<li>The Law of Cosines is useful for many types of applied problems. The first step in solving such problems is generally to draw a sketch of the problem presented. If the information given fits one of the three models (the three equations), then apply the Law of Cosines to find a solution.<\/li>\n<li>Heron\u2019s formula allows the calculation of area in oblique triangles. All three sides must be known to apply Heron\u2019s formula.<\/li>\n<\/ul>\n<div>\n<dl id=\"fs-id1165133184256\" class=\"definition\">\n<dd id=\"fs-id1165133184261\"><\/dd>\n<dd>\n<dl id=\"fs-id1165133184256\" class=\"definition\">\n<dd>\n<h2>Glossary<\/h2>\n<dl id=\"fs-id1165135690077\" class=\"definition\">\n<dt>Law of Cosines<\/dt>\n<dd id=\"fs-id1165135690083\">states that the square of any side of a triangle is equal to the sum of the squares of the other two sides minus twice the product of the other two sides and the cosine of the included angle<\/dd>\n<\/dl>\n<dl id=\"fs-id1165133184256\" class=\"definition\">\n<dt>Generalized Pythagorean Theorem<\/dt>\n<dd id=\"fs-id1165133184261\">an extension of the Law of Cosines; relates the sides of an oblique triangle and is used for SAS and SSS triangles<\/dd>\n<\/dl>\n<\/dd>\n<\/dl>\n<dl id=\"fs-id1165133184256\" class=\"definition\">\n<dd id=\"fs-id1165133184261\"><\/dd>\n<\/dl>\n<\/dd>\n<\/dl>\n<\/div>\n\n\t\t\t <section class=\"citations-section\" role=\"contentinfo\">\n\t\t\t <h3>Candela Citations<\/h3>\n\t\t\t\t\t <div>\n\t\t\t\t\t\t <div id=\"citation-list-212\">\n\t\t\t\t\t\t\t <div class=\"licensing\"><div class=\"license-attribution-dropdown-subheading\">CC licensed content, Specific attribution<\/div><ul class=\"citation-list\"><li>Precalculus. <strong>Authored by<\/strong>: OpenStax College. <strong>Provided by<\/strong>: OpenStax. <strong>Located at<\/strong>: <a target=\"_blank\" href=\"http:\/\/cnx.org\/contents\/fd53eae1-fa23-47c7-bb1b-972349835c3c@5.175:1\/Preface\">http:\/\/cnx.org\/contents\/fd53eae1-fa23-47c7-bb1b-972349835c3c@5.175:1\/Preface<\/a>. <strong>License<\/strong>: <em><a target=\"_blank\" rel=\"license\" href=\"https:\/\/creativecommons.org\/licenses\/by\/4.0\/\">CC BY: Attribution<\/a><\/em><\/li><\/ul><\/div>\n\t\t\t\t\t\t <\/div>\n\t\t\t\t\t <\/div>\n\t\t\t <\/section>","protected":false},"author":23485,"menu_order":3,"template":"","meta":{"_candela_citation":"[{\"type\":\"cc-attribution\",\"description\":\"Precalculus\",\"author\":\"OpenStax College\",\"organization\":\"OpenStax\",\"url\":\"http:\/\/cnx.org\/contents\/fd53eae1-fa23-47c7-bb1b-972349835c3c@5.175:1\/Preface\",\"project\":\"\",\"license\":\"cc-by\",\"license_terms\":\"\"}]","CANDELA_OUTCOMES_GUID":"","pb_show_title":"on","pb_short_title":"","pb_subtitle":"","pb_authors":[],"pb_section_license":""},"chapter-type":[],"contributor":[],"license":[],"class_list":["post-212","chapter","type-chapter","status-publish","hentry"],"part":210,"_links":{"self":[{"href":"https:\/\/courses.lumenlearning.com\/gsu-precalculus\/wp-json\/pressbooks\/v2\/chapters\/212","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/courses.lumenlearning.com\/gsu-precalculus\/wp-json\/pressbooks\/v2\/chapters"}],"about":[{"href":"https:\/\/courses.lumenlearning.com\/gsu-precalculus\/wp-json\/wp\/v2\/types\/chapter"}],"author":[{"embeddable":true,"href":"https:\/\/courses.lumenlearning.com\/gsu-precalculus\/wp-json\/wp\/v2\/users\/23485"}],"version-history":[{"count":5,"href":"https:\/\/courses.lumenlearning.com\/gsu-precalculus\/wp-json\/pressbooks\/v2\/chapters\/212\/revisions"}],"predecessor-version":[{"id":795,"href":"https:\/\/courses.lumenlearning.com\/gsu-precalculus\/wp-json\/pressbooks\/v2\/chapters\/212\/revisions\/795"}],"part":[{"href":"https:\/\/courses.lumenlearning.com\/gsu-precalculus\/wp-json\/pressbooks\/v2\/parts\/210"}],"metadata":[{"href":"https:\/\/courses.lumenlearning.com\/gsu-precalculus\/wp-json\/pressbooks\/v2\/chapters\/212\/metadata\/"}],"wp:attachment":[{"href":"https:\/\/courses.lumenlearning.com\/gsu-precalculus\/wp-json\/wp\/v2\/media?parent=212"}],"wp:term":[{"taxonomy":"chapter-type","embeddable":true,"href":"https:\/\/courses.lumenlearning.com\/gsu-precalculus\/wp-json\/pressbooks\/v2\/chapter-type?post=212"},{"taxonomy":"contributor","embeddable":true,"href":"https:\/\/courses.lumenlearning.com\/gsu-precalculus\/wp-json\/wp\/v2\/contributor?post=212"},{"taxonomy":"license","embeddable":true,"href":"https:\/\/courses.lumenlearning.com\/gsu-precalculus\/wp-json\/wp\/v2\/license?post=212"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}