# 6.4: Adding and Subtracting Polynomials

**At Grade**Created by: CK-12

**Practice**Addition and Subtraction of Polynomials

Rectangular prism A has a volume of \begin{align*}x^3 +2x^2 - 3\end{align*}. Rectangular prism B has a volume of \begin{align*}x^4 + 2x^3 - 8x^2\end{align*}. How much larger is the volume of rectangular prism B than rectangular prism A?

### Watch This

James Sousa: Ex: Intro to Polynomials in One Variable

### Guidance

A **polynomial** is an expression with multiple variable terms, such that the exponents are greater than or equal to zero. All quadratic and linear equations are polynomials. Equations with negative exponents, square roots, or variables in the denominator are not polynomials.

Now that we have established what a polynomial is, there are a few important parts. Just like with a quadratic, a polynomial can have a **constant**, which is a number without a variable. The **degree** of a polynomial is the largest exponent. For example, all quadratic equations have a degree of 2. Lastly, the **leading coefficient** is the coefficient in front of the variable with the degree. In the polynomial \begin{align*}4x^4 + 5x^3 -8x^2 + 12x +24\end{align*} above, the degree is 4 and the leading coefficient is also 4. Make sure that when finding the degree and leading coefficient you have the polynomial in standard form. **Standard form** lists all the variables in order, from greatest to least.

#### Example A

Rewrite \begin{align*}x^3 -5x^2 + 12x^4 + 15 -8x\end{align*} in standard form and find the degree and leading coefficient.

**Solution:** To rewrite in standard form, put each term in order, from greatest to least, according to the exponent. Always write the constant last.

\begin{align*}x^3 -5x^2 + 12x^4 + 15 -8x \rightarrow 12x^4 + x^3 -5x^2 -8x + 15\end{align*}

Now, it is easy to see the leading coefficient, 12, and the degree, 4.

#### Example B

Simplify \begin{align*}(4x^3 -2x^2 + 4x + 15) + (x^4 -8x^3 -9x-6)\end{align*}

**Solution:** To add or subtract two polynomials, combine like terms. **Like terms** are any terms where the exponents of the variable are the same. We will regroup the polynomial to show the like terms.

\begin{align*}& (4x^3 -2x^2 + 4x + 15) + (x^4 -8x^3 -9x -6)\\ & x^4 + (4x^3 -8x^3) -2x^2 + (4x -9x) + (15-6)\\ & x^4 -4x^3 -2x^2 -5x + 9\end{align*}

#### Example C

Simplify \begin{align*}(2x^3 + x^2 -6x -7)-(5x^3 -3x^2 + 10x -12)\end{align*}

**Solution:** When subtracting, distribute the negative sign to every term in the second polynomial, then combine like terms.

\begin{align*}& (2x^3 + x^2 -6x -7)-(5x^3 -3x^2 +10x -12)\\ & 2x^3 + x^2 -6x -7 -5x^3 + 3x^2 -10x + 12\\ & (2x^3 -5x^3) + (x^2 + 3x^2) + (-6x -10x) + (-7 + 12)\\ & -3x^3 + 4x^2 -16x + 5\end{align*}

**Intro Problem Revisit**

We need to subtract the volume of rectangular prism A from the volume of rectangular prism B.

\begin{align*}(x^4 + 2x^3 - 8x^2) - (x^3 + 2x^2 - 3)\\ = x^4 + 2x^3 - 8x^2 - x^3 - 2x^2 + 3 \\ = x^4 + x^3 - 10x^2 + 3\end{align*}.

Therefore, the difference between the two volumes is \begin{align*}x^4 + x^3 - 10x^2 + 3\end{align*}.

### Guided Practice

1. Is \begin{align*}\sqrt{2x^3 -5x} + 6\end{align*} a polynomial? Why or why not?

2. Find the leading coefficient and degree of \begin{align*}6x^2 -3x^5 + 16x^4 + 10x -24\end{align*}.

Add or subtract.

3. \begin{align*}(9x^2 + 4x^3 -15x + 22)+(6x^3 -4x^2 + 8x -14)\end{align*}

4. \begin{align*}(7x^3 + 20x -3)-(x^3 -2x^2 + 14x -18)\end{align*}

#### Answers

1. No, this is not a polynomial because \begin{align*}x\end{align*} is under a square root in the equation.

2. In standard form, this polynomial is \begin{align*}-3x^5 + 16x^4 + 6x^2 + 10x -24\end{align*}. Therefore, the degree is 5 and the leading coefficient is -3.

3. \begin{align*}(9x^2 + 4x^3 -15x + 22)+(6x^3 -4x^2 + 8x -14) = 10x^3 + 5x^2 -7x + 8\end{align*}

4. \begin{align*}(7x^3 + 20x -3)-(x^3 -2x^2 + 14x -18) = 6x^3 + 2x^2 + 6x + 15\end{align*}

### Vocabulary

- Polynomial
- An expression with multiple variable terms, such that the exponents are greater than or equal to zero.

- Constant
- A number without a variable in a mathematical expression.

- Degree(of a polynomial)
- The largest exponent in a polynomial.

- Leading coefficient
- The coefficient in front of the variable with the degree.

- Standard form
- Lists all the variables in order, from greatest to least.

- Like terms
- Any terms where the exponents of the variable are the same.

### Practice

Determine if the following expressions are polynomials. If not, state why. If so, write in standard form and find the degree and leading coefficient.

- \begin{align*}\frac{1}{x^2} + x + 5\end{align*}
- \begin{align*}x^3 + 8x^4 -15x + 14x^2 -20\end{align*}
- \begin{align*}x^3 + 8\end{align*}
- \begin{align*}5x^{-2} + 9x^{-1} + 16\end{align*}
- \begin{align*}x^2 \sqrt{2} - x\sqrt{6} + 10\end{align*}
- \begin{align*}\frac{x^4 + 8x^2 +12}{3}\end{align*}
- \begin{align*}\frac{x^2-4}{x}\end{align*}
- \begin{align*}-6x^3 + 7x^5 -10x^6 + 19x^2 -3x +41\end{align*}

Add or subtract the following polynomials.

- \begin{align*}(x^3 + 8x^2 -15x + 11) + (3x^3 -5x^2 -4x + 9)\end{align*}
- \begin{align*}(-2x^4 + x^3 + 12x^2 + 6x -18)-(4x^4 -7x^3 + 14x^2 + 18x -25)\end{align*}
- \begin{align*}(10x^3 -x^2 + 6x + 3) + (x^4 -3x^3 + 8x^2 -9x + 16)\end{align*}
- \begin{align*}(7x^3 -2x^2 + 4x -5)-(6x^4 + 10x^3 + x^2 + 4x -1)\end{align*}
- \begin{align*}(15x^2 + x -27) + (3x^3 -12x + 16)\end{align*}
- \begin{align*}(2x^5 -3x^4 + 21x^2 + 11x -32)-(x^4 -3x^3 -9x^2 + 14x -15)\end{align*}
- \begin{align*}(8x^3 -13x^2 + 24)-(x^3 + 4x^2 -2x + 17) + (5x^2 + 18x -19)\end{align*}

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Term | Definition |
---|---|

constant |
A constant is a value that does not change. In Algebra, this is a number such as 3, 12, 342, etc., as opposed to a variable such as x, y or a. |

Degree |
The degree of a polynomial is the largest exponent of the polynomial. |

distributive property |
The distributive property states that the product of an expression and a sum is equal to the sum of the products of the expression and each term in the sum. For example, . |

Leading coefficient |
The leading coefficient of a polynomial is the coefficient of the variable with the highest degree. |

like terms |
Terms are considered like terms if they are composed of the same variables with the same exponents on each variable. |

Polynomial |
A polynomial is an expression with at least one algebraic term, but which does not indicate division by a variable or contain variables with fractional exponents. |

Standard form |
The standard form of a polynomial lists all the terms in order, from highest degree to lowest degree. |

### Image Attributions

Here you'll learn how to add and subtract polynomials, as well as learn about the different parts of a polynomial.