Key Concepts

• Given two points, we can find the slope of a line using the slope formula.
• We can identify the slope and $y$-intercept of an equation in slope-intercept form.
• We can find the equation of a line given the slope and a point.
• We can also find the equation of a line given two points. Find the slope and use point-slope form.
• The standard form of a line has no fractions.
• Horizontal lines have a slope of zero and are defined as $y=c$, where c is a constant.
• Vertical lines have an undefined slope (zero in the denominator) and are defined as $x=c$, where c is a constant.
• Parallel lines have the same slope and different $y$–intercepts.
• Perpendicular lines have slopes that are negative reciprocals of each other unless one is horizontal and the other is vertical.

Glossary

slope

the change in $y$–values over the change in $x$–values