Prealgebra

Module 2: The Language of Algebra

Simplifying Algebraic Expressions

Learning Outcomes

Identify the variables and constants in a term
Identify the coefficient of a variable term
Identify and combine like terms in an expression

Identify Terms, Coefficients, and Like Terms

Algebraic expressions are made up of terms. A term is a constant or the product of a constant and one or more variables. Some examples of terms are

7,y,5{x}^{2},9a,\text{and }13xy

.

The constant that multiplies the variable(s) in a term is called the coefficient. We can think of the coefficient as the number in front of the variable. The coefficient of the term

3x

3

. When we write

x

, the coefficient is

1

, since

x=1\cdot x

. The table below gives the coefficients for each of the terms in the left column.

Term	Coefficient
$7$	$7$
$9a$	$9$
$y$	$1$
$5{x}^{2}$	$5$

An algebraic expression may consist of one or more terms added or subtracted. In this chapter, we will only work with terms that are added together. The table below gives some examples of algebraic expressions with various numbers of terms. Notice that we include the operation before a term with it.

Expression	Terms
$7$	$7$
$y$	$y$
$x+7$	$x,7$
$2x+7y+4$	$2x,7y,4$
$3{x}^{2}+4{x}^{2}+5y+3$	$3{x}^{2},4{x}^{2},5y,3$

example

Identify each term in the expression

9b+15{x}^{2}+a+6

. Then identify the coefficient of each term.

Solution:

The expression has four terms. They are

9b,15{x}^{2},a

, and

6

The coefficient of
$9b$
is
$9$
.
The coefficient of
$15{x}^{2}$
is
$15$
.
Remember that if no number is written before a variable, the coefficient is
$1$
. So the coefficient of
$a$
is
$1$
.
The coefficient of a constant is the constant, so the coefficient of
$6$
is
$6$
.

try it

Some terms share common traits. Look at the following terms. Which ones seem to have traits in common?

5x,7,{n}^{2},4,3x,9{n}^{2}

Which of these terms are like terms?

The terms
$7$
and
$4$
are both constant terms.
The terms
$5x$
and
$3x$
are both terms with
$x$
.
The terms
${n}^{2}$
and
$9{n}^{2}$
both have
${n}^{2}$
.

Terms are called like terms if they have the same variables and exponents. All constant terms are also like terms. So among the terms

5x,7,{n}^{2},4,3x,9{n}^{2}

$7$
and
$4$
are like terms.
$5x$
and
$3x$
are like terms.
${n}^{2}$
and
$9{n}^{2}$
are like terms.

Like Terms

Terms that are either constants or have the same variables with the same exponents are like terms.

example

Identify the like terms:

${y}^{3},7{x}^{2},14,23,4{y}^{3},9x,5{x}^{2}$
$4{x}^{2}+2x+5{x}^{2}+6x+40x+8xy$

Show Solution

Solution:

1.

{y}^{3},7{x}^{2},14,23,4{y}^{3},9x,5{x}^{2}

Look at the variables and exponents. The expression contains

{y}^{3},{x}^{2},x

, and constants.

The terms

{y}^{3}

and

4{y}^{3}

are like terms because they both have

{y}^{3}

.

The terms

7{x}^{2}

and

5{x}^{2}

are like terms because they both have

{x}^{2}

.

The terms

14

and

23

are like terms because they are both constants.

The term

9x

does not have any like terms in this list since no other terms have the variable

x

raised to the power of

1

.

2.

4{x}^{2}+2x+5{x}^{2}+6x+40x+8xy

Look at the variables and exponents. The expression contains the terms

4{x}^{2},2x,5{x}^{2},6x,40x,\text{and}8xy

The terms

4{x}^{2}

and

5{x}^{2}

are like terms because they both have

{x}^{2}

.

The terms

2x,6x,\text{and}40x

are like terms because they all have

x

.

The term

8xy

has no like terms in the given expression because no other terms contain the two variables

xy

try it

Simplify Expressions by Combining Like Terms

We can simplify an expression by combining the like terms. What do you think

3x+6x

would simplify to? If you thought

9x

, you would be right!

We can see why this works by writing both terms as addition problems.

The image shows the expression 3 x plus 6 x. The 3 x represents x plus x plus x. The 6 x represents x plus x plus x plus x plus x plus x. The expression 3 x plus 6 x becomes x plus x plus x plus x plus x plus x plus x plus x plus x. This simplifies to a total of 9 x's or the term 9 x.

The image shows the expression 3 x plus 6 x. The 3 x represents x plus x plus x. The 6 x represents x plus x plus x plus x plus x plus x. The expression 3 x plus 6 x becomes x plus x plus x plus x plus x plus x plus x plus x plus x. This simplifies to a total of 9 x's or the term 9 x.

Add the coefficients and keep the same variable. It doesn’t matter what

x

is. If you have

3

of something and add

6

more of the same thing, the result is

9

of them. For example,

3

oranges plus

6

oranges is

9

oranges. We will discuss the mathematical properties behind this later.

The expression

3x+6x

has only two terms. When an expression contains more terms, it may be helpful to rearrange the terms so that like terms are together. The Commutative Property of Addition says that we can change the order of addends without changing the sum. So we could rearrange the following expression before combining like terms.

The image shows the expression 3 x plus 4 y plus 2 x plus 6 y. The position of the middle terms, 4 y and 2 x, can be switched so that the expression becomes 3 x plus 2 x plus 4 y plus 6 y. Now the terms containing x are together and the terms containing y are together.

The image shows the expression 3 x plus 4 y plus 2 x plus 6 y. The position of the middle terms, 4 y and 2 x, can be switched so that the expression becomes 3 x plus 2 x plus 4 y plus 6 y. Now the terms containing x are together and the terms containing y are together.

Now it is easier to see the like terms to be combined.

Combine like terms

Identify like terms.
Rearrange the expression so like terms are together.
Add the coefficients of the like terms.

example

Simplify the expression:

3x+7+4x+5

Show Solution

Solution:

	$3x+7+4x+5$
Identify the like terms.	$\color{red}{3x}+\color{blue}{7}+\color{red}{4x}+\color{blue}{5}$
Rearrange the expression, so the like terms are together.	$\color{red}{3x}+\color{red}{4x}+\color{blue}{7}+\color{blue}{5}$
Add the coefficients of the like terms.
The original expression is simplified to...	$7x+12$

try it

example

Simplify the expression:

8x+7{x}^{2}-{x}^{2}-+4x

Show Solution

Solution:

	$8x+7{x}^{2}-{x}^{2}-+4x$
Identify the like terms.
Rearrange the expression so like terms are together.
Add the coefficients of the like terms.

These are not like terms and cannot be combined. So

8{x}^{2}+12x

is in simplest form.

try it

In the following video, we present more examples of how to combine like terms given an algebraic expression.

Licenses and Attributions

CC licensed content, Shared previously

Ex 1: Combining Like Terms. Authored by: James Sousa (Mathispower4u.com). License: CC BY: Attribution
Ex 2: Combining Like Terms. Authored by: James Sousa (Mathispower4u.com). License: CC BY: Attribution
Question ID: 144899, 144900, 144905,146540. Authored by: Alyson Day. License: CC BY: Attribution. License terms: IMathAS Community License CC-BY + GPL

CC licensed content, Specific attribution

Prealgebra. Provided by: OpenStax. License: CC BY: Attribution. License terms: Download for free at http://cnx.org/contents/[email protected]

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