Learning Objectives
- Identify the terms, the coefficients, and the exponents of a polynomial
- Evaluate a polynomial for given values of the variable
Identify the terms, the coefficients, and the exponents of a polynomial
Polynomials are algebraic expressions that are created by combining numbers and variables using arithmetic operations such as addition, subtraction, multiplication, division, and exponentiation. You can create a polynomial by adding or subtracting terms. Polynomials are very useful in applications from science and engineering to business. You may see a resemblance between expressions, which we have been studying in this course, and polynomials. Polynomials are a special sub-group of mathematical expressions and equations.
The following table is intended to help you tell the difference between what is a polynomial and what is not.
| IS a Polynomial | Is NOT a Polynomial | Because |
| [latex]2x^2-\frac{1}{2}x -9[/latex] | [latex]\frac{2}{x^{2}}+x[/latex] | Polynomials only have variables in the numerator |
| [latex]\frac{y}{4}-y^3[/latex] | [latex]\frac{2}{y}+4[/latex] | Polynomials only have variables in the numerator |
| [latex]\sqrt{12}\left(a\right)+9[/latex] | [latex]\sqrt{a}+7[/latex] | Variables under a root are not allowed in polynomials |
The basic building block of a polynomial is a monomial. A monomial is one term and can be a number, a variable, or the product of a number and variables with an exponent. The number part of the term is called the coefficient.
Examples of monomials:
- number: [latex]{2}[/latex]
- variable: [latex]{x}[/latex]
- product of number and variable: [latex]{2x}[/latex]
- product of number and variable with an exponent: [latex]{2x}^{3}[/latex]
The coefficient can be any real number, including 0. The exponent of the variable must be a whole number—0, 1, 2, 3, and so on. A monomial cannot have a variable in the denominator or a negative exponent.
The value of the exponent is the degree of the monomial. Remember that a variable that appears to have no exponent really has an exponent of 1. And a monomial with no variable has a degree of 0. (Since [latex]x^{0}[/latex] has the value of 1 if [latex]x\neq0[/latex], a number such as 3 could also be written [latex]3x^{0}[/latex], if [latex]x\neq0[/latex] as [latex]3x^{0}=3\cdot1=3[/latex].)
Example
Identify the coefficient, variable, and degree of the variable for the following monomial terms:
1) 9
2) x
3) [latex] \displaystyle \frac{3}{5}{{k}^{8}}[/latex]
A polynomial is a monomial or the sum or difference of two or more polynomials. Each monomial is called a term of the polynomial.
Some polynomials have specific names indicated by their prefix.
- monomial—is a polynomial with exactly one term (“mono”—means one)
- binomial—is a polynomial with exactly two terms (“bi”—means two)
- trinomial—is a polynomial with exactly three terms (“tri”—means three)
The word “polynomial” has the prefix, “poly,” which means many. However, the word polynomial can be used for all numbers of terms, including only one term.
Because the exponent of the variable must be a whole number, monomials and polynomials cannot have a variable in the denominator.
Polynomials can be classified by the degree of the polynomial. The degree of a polynomial is the degree of its highest degree term. So the degree of [latex]2x^{3}+3x^{2}+8x+5[/latex] is 3.
A polynomial is said to be written in standard form when the terms are arranged from the highest degree to the lowest degree. When it is written in standard form it is easy to determine the degree of the polynomial.
The table below illustrates some examples of monomials, binomials, trinomials, and other polynomials. They are all written in standard form.
| Monomials | Binomials | Trinomials | Other Polynomials |
| 15 | [latex]3y+13[/latex] | [latex]x^{3}-x^{2}+1[/latex] | [latex]5x^{4}+3x^{3}-6x^{2}+2x[/latex] |
| [latex] \displaystyle \frac{1}{2}x[/latex] | [latex]4p-7[/latex] | [latex]3x^{2}+2x-9[/latex] | [latex]\frac{1}{3}x^{5}-2x^{4}+\frac{2}{9}x^{3}-x^{2}+4x-\frac{5}{6}[/latex] |
| [latex]-4y^{3}[/latex] | [latex]3x^{2}+\frac{5}{8}x[/latex] | [latex]3y^{3}+y^{2}-2[/latex] | [latex]3t^{3}-3t^{2}-3t-3[/latex] |
| [latex]16n^{4}[/latex] | [latex]14y^{3}+3y[/latex] | [latex]a^{7}+2a^{5}-3a^{3}[/latex] | [latex]q^{7}+2q^{5}-3q^{3}+q[/latex] |
When the coefficient of a polynomial term is 0, you usually do not write the term at all (because 0 times anything is 0, and adding 0 doesn’t change the value). The last binomial above could be written as a trinomial, [latex]14y^{3}+0y^{2}+3y[/latex].
A term without a variable is called a constant term, and the degree of that term is 0. For example 13 is the constant term in [latex]3y+13[/latex]. You would usually say that [latex]14y^{3}+3y[/latex] has no constant term or that the constant term is 0.
Example
For the following expressions, determine whether they are a polynomial. If so, categorize them as a monomial, binomial, or trinomial.
- [latex]\frac{x-3}{1-x}+x^2[/latex]
- [latex]t^2+2t-3[/latex]
- [latex]x^3+\frac{x}{8}[/latex]
- [latex]\frac{\sqrt{y}}{2}-y-1[/latex]
In the following video, you will be shown more examples of how to identify and categorize polynomials.
Evaluate a polynomial for given values of the variable
You can evaluate polynomials just as you have been evaluating expressions all along. To evaluate an expression for a value of the variable, you substitute the value for the variable every time it appears. Then use the order of operations to find the resulting value for the expression.
Example
Evaluate [latex]3x^{2}-2x+1[/latex] for [latex]x=-1[/latex].
Example
Evaluate [latex] \displaystyle -\frac{2}{3}p^{4}+2p^{3}-p[/latex] for [latex]p = 3[/latex].
The following video presents more examples of evaluating a polynomial for a given value.