Factoring The Difference of 2 Squares

After studying this lesson, you will be able to:

• Factor the difference of two squares.

Steps of Factoring:

1. Factor out the GCF

2. Look at the number of terms:

• 2 Terms: Look for the Difference of 2 Squares
• 3 Terms: Factor the Trinomial
• 4 Terms: Factor by Grouping

3. Factor Completely

4. Check by Multiplying

This lesson will concentrate on the second step of factoring:Factoring the Difference of 2 Squares.

**When there are 2 terms, we look for the difference of 2squares. Don't forget to look for a GCF first.**

We have the difference of two squares when the following aretrue:

There are 2 terms separated by a minus sign

To factor the difference of 2 squares, we write 2 parentheses.One will have an addition sign and the other will have asubtraction sign like this:

Next, we find the square root of the first term. We put thesein the first positions. Then, we find the square root of theconstant term and we put these in the last positions.

Example 1

Factor

There is no GCF other than one. This is the difference of twosquares. Now we take the square root of the first term. Thesquare root of ¼ x ² is so we put in the first positions:

Now we take the square root of the constant term. The squareroot of is y so we put in the last positions.Now, the problem is completely factored.

Check by using FOIL

Example 2

Factor 12x ³ - 27xy ²

There is a GCF in this problem. Therefore, we have to factorout the GCF first. The GCF is 3x so we factor that out.

3x (4x ² - 9y ²)

Now we have the difference of two squares remaining in theparentheses. We have to factor completely so we factor thedifference of two squares.....keeping the GCF.

3x (2x + 3y ) (2x - 3y )

Check (it will take two steps to check) First forget about the3x for the time being and FOIL the 2 binomials:

(2x + 3y) (2x - 3y) 4x ² - 6xy +6xy - 9y ² which is 4x ² - 9y ²

Now multiply the result by 3x:

3x (4x ² - 9y ²) 12x ³ - 27xy²

Example 3

Factor 162x ⁴ - 32y⁸

There is a GCF in this problem. Therefore, we have to factorout the GCF first. The GCF is 2 so we factor that out.

2(81x ⁴ - 16y⁸ )

Now we have the difference of two squares remaining in theparentheses. We have to factor completely so we factor thedifference of two squares.....keeping the GCF.

2(9x ² + 4y⁴ ) (9x ² - 4y⁴)

The second parenthesis still contains the difference of 2squares so we have to factor that again. We keep the GCF and thefirst parenthesis.

2(9x ² + 4y⁴ ) (3x + 2y ) (3x - 2y )

This is now factored completely.

Check (it will take three steps to check) First forget aboutthe 2 and the first binomial for the time being and FOIL the last2 binomials:

(3x + 2y ) (3x - 2y ) (9x ² - 4y⁴)

Now multiply the 2 remaining binomials:

(9x ² + 4y⁴ ) (9x ² - 4y⁴) (81x ⁴ - 16y⁸)

Now multiply the result by 2:

2(81x ⁴ - 16y⁸ ) 162x ⁴ - 32y⁸