# 2.11: Synthetic Division of Polynomials

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

**Practice**Synthetic Division of Polynomials

If you have completed the lesson on oblique asymptotes, you probably know that the problem:

*
Find the oblique asymptote of
*

could be an excellent reason to groan and grumble due to the long division that would be required.

Isn't there a better way?

### Watch This

Embedded Video:

- James Sousa: Polynomial Division: Synthetic Division

### Guidance

**
Synthetic Division
**

In this lesson, we explore
*
synthetic division
*
, a derivative of
*
polynomial long division
*
.

To illustrate the value of synthetic division, we will first solve an example with long division and then redo the division by the synthetic division method.

#### Example A

Divide: by .

**
Solution A: long division
**

**
Solution B: synthetic division
**

As you can see, all the math involved relates only to the coefficients of the variables and the constants. We could just as easily complete the division by omitting the variables, as long as we write the coefficients in the proper places.

Doing that, the problem looks like this:

Since the underlined numerals are repetitions of those immediately above them, we can shorten the process by simply deleting them. Further, since these underlined numbers are products of the numbers in the quotient by the 1 in the divisor, we eliminate this 1.

Thus we get the following

It is also unnecessary to bring down the -10 and 13:

Moving the numerals upward, we get

When the numeral 1 (the first number in the quotient) is brought down to the last line, it will contain the remainder and the quotient,

Therefore, the quotient is and the remainder is . This is synthetic division'.

#### Example B

Use synthetic division to find the quotient and the remainder of

**
Solution
**

First we write the divisor in the form , as . Then use -2 as a “divisor” in the synthetic division as follows:

Notice that 0 is used as the coefficient of the “missing” term. Also, we wrote the coefficients of the dividend in descending order. The process of synthetic division is as follows: Bring down the first coefficient 3 and multiply by -2 (the divisor) to get -6, and then add 0 to -6 to get -6. Next, multiply -6 by -2 (the divisor) to get 12, and then add -8 to 12 to get 4. Finally, multiply 4 by -2 to get -8, and then add 1 to -8 to get the remainder, -7. As a result of this process, the quotient is

and the remainder is

In other words, since

Remember, this method will only work when the divisor is in the form , that is, when the coefficient of in the divisor is 1.

#### Example C

If , evaluate

**
Solution
**

We can simply use the synthetic division to evaluate at the given values. By the remainder theorem, the remainder is equal to .

- Using synthetic division,

Hence, .

- By synthetic division,

Hence, .

- By synthetic division,

Hence, .

### Vocabulary

**
Synthetic division
**
is a concise 'shortcut' method of dividing polynomials.

**
Polynomial long division
**
is the standard method of long division, applied to the division of polynomials.

A
**
Dividend
**
is the number (or polynomial) being divided, a

**is the number (or polynomial) being divided 'into' the dividend, and a**

*divisor***is the result, occasionally with a**

*quotient***(the amount left over after all the even division has been completed).**

*remainder*### Guided Practice

**
Problems
**

**
Divide using Long Division:
**

1)

2)

**
Divide using Synthetic Division:
**

3)

**
Solutions
**

1) Solved in the video below:

- KhanAcademy: Algebraic Long Division

2) Solved in the video below:

- KhanAcademy: Dividing Polynomials with Remainders

3) Solved in the video below:

- clindelof: Synthetic Division One

### Practice

**
Divide by using long division:
**

- divided by
- divided by
- divided by

**
Divide using synthetic division:
**

- divided by
- divided by
- divided by
- divided by
- divided by

**
Use synthetic substitution to evaluate the polynomial function for the given value:
**

- for
- for
- for
- The area of a rectangle is and the length is What is the width?
- A group of geologists have taken a collection of samples of a substance from a proposed mining site and must identify the substance. Each sample is roughly cylindrical. The volume of each sample as a function of cylinder height (in centimeters) is . The mass (in grams) of each sample in terms of height an be modeled by . Write an expression that represents the density of the samples. (Hint: )

### Image Attributions

## Description

## Learning Objectives

Here you will explore how to use long division and a 'shortcut' version of long division called 'synthetic division' to help find the
*
x
*
-intercepts of higher-degree polynomials.