Unit 6 Factoring Polynomials

Greatest Common Factor Factoring by Grouping (Four Terms) AC Method (3 Terms) Difference of Two Squares (2 Terms) Sum and Difference of Two Cubes (2

Terms)

Why do I need to be able to factor?

• We need to be able to factor in order to

Solve quadratic equations.Work with Rational Expressions

What is factoring?

• Factoring is the OPPOSITE of distribution

• When we factor, we are taking apart a polynomial

What are factors?

Each piece that we take apart is called a factor

FACTORS are terms that are multiplied together to reach a PRODUCT (this is a code word for multiplication). Factors can be numbers, variables, and quantities (binomials or larger within parentheses).

Does every polynomial factor?

• No … some polynomials (or numbers for that matter) do not factor!

• Things that do not factor are called PRIME

The Factoring Process

• There are MANY ways to teach/discuss factoring polynomials.

• If you have a way that works for you that you understand then you should feel no pressure to do it any other way.

• If you don’t have a method or you are interested in seeing a different process, I promise you mine works every time.

SHERRIE’S PROCESS FOR FACTORING POLYNOMIALSFactor out the GCF first

There might not be a GCF (other than 1).Just because there is a GCF factored out does

not mean you are done.Just because you did not factor out a GCF does

not mean the polynomial is prime.GCF can be a number, a letter, a number-letter

combination, or a polynomial.

WARNING

Factoring out the GCF does not mean you are done factoring … it is only step 1!

You might be done … but you might not!

Just in case I was not clear earlier!

SHERRIE’S PROCESS FOR FACTORING POLYNOMIALS

Count the number of terms

If 4 terms: Use the grouping methodIf 3 terms: Use the AC methodIf 2 terms: Use the recipe method

SHERRIE’S PROCESS FOR FACTORING POLYNOMIALS

Last step … double check to make sure none of the polynomial terms can be factored (this is especially important if you did not factor a GCF out first).

As a reminder … you should be able to multiply your factors and get a product that is equal to the original polynomial.

Example of GCF of Polynomial

Factor 7x2 - 14xy 1. Find the GCF of the terms 7x2 and

14xy 7x2 = 14xy = The GCF is:

Example of GCF of Polynomial

Factor 7x2 - 14xy 1. Find the GCF of the terms 7x2 and 14xy The GCF is 7x

2. Divide each term in the polynomial by the GCF you just chose.

7x2

-14xyAnswer:

Example of GCF of Polynomial

Factor 7x2 - 14xy 1. Find the GCF of the terms 7x2 and 14xy The GCF is 7x2. Divide each term in the polynomial by the GCF you just

chose. Answer: (x – 2y)

3. Write the GCF followed by the result from step 2 IN PARENTHESES.

4 Term Polynomials

Example: Factor ax + ay + 5x + 5y

4 Term Polynomials

Example: Factor ax + ay + 5x + 5y

If you look carefully, there is no GCF larger than 1 common to all FOUR terms. Since we never factor out a plain 1 (since it changes nothing), we need to find another way to approach this problem.

4 Term Polynomials

Example: Factor ax + ay + 5x + 5y1. Factor out GCF: There was none.

2. Pair up the terms in such a way that each pair has something in common. Many times the pairs work out to be the first two and the second two, but don’t be afraid to use the commutative property and shuffle things around! Then make TWO groups by drawing a vertical line separating the first two terms with the second two terms.

ax + ay + 5x + 5y

4 Term Polynomials

Example: Factor ax + ay + 5x + 5y1. Factor out GCF: There was none.

2. Make two groups

3. Factor the GCF from each pair, as if they were completely different problems.

ax + ay + 5x + 5y

4 Term Polynomials

Example: Factor ax + ay + 5x + 5y1. Factor out GCF: There was none.

2. Make two groups

3. Factor the GCF from each pair. a(x + y) + 5(x + y) 4. Factor the common factor from the two groups.

a(x + y) + 5(x + y)

(x + y)(a + 5) OR (a + 5)(x + y)

4 Term Polynomials

Example: Factor 5a - 2x + 10 - ax

4 Term Polynomials

Example: Factor 5a - 2x + 10 - ax

If you look carefully, there is no GCF larger than 1 common to all FOUR terms. Since we never factor out a plain 1 (since it changes nothing), we need to find another way to approach this problem.

4 Term Polynomials

Example: Factor 5a - 2x + 10 - ax 1. Factor out GCF: There was none.

2. Pair up the terms in such a way that each pair has something in common. Many times the pairs work out to be the first two and the second two, but don’t be afraid to use the commutative property and shuffle things around! Then make TWO groups by drawing a vertical line separating the first two terms with the second two terms.

5a - 2x + 10 - ax Looking at both the left group and the right group, I

do not see any GCF in either group that can be factored out … lets rearrange the terms to see if we can find something that will work.

5a - ax + 10 - 2x

4 Term Polynomials

Example: Factor 5a - 2x + 10 - ax 1. Factor out GCF: There was none.

2. Make two groups

3. Factor the GCF from each pair, as if they were completely different problems.

5a - 2x + 10 - ax

4 Term Polynomials

Example: Factor 5a - 2x + 10 - ax 1. Factor out GCF: There was none.

2. Make two groups

3. Factor the GCF from each pair. a(5 - x) + 2(5 - x) 4. Factor the common factor from the two groups.

a(5 - x) + 2(5 - x)

(a + 2)(5 - x) OR (5 - x)(a + 2)

• As we transition from FOUR term polynomials to THREE term polynomials … we are going to use our new GROUPING method.

3 Term PolynomialsAC METHOD (FACTORING 3 TERM POLYNOMIALS)

STEP1: Make sure the polynomial is in standard form (exponents in descending order) …

STEP2: Factor out the GCF STEP3: Label the value for a, b, and c STEP4: We are trying to find a pair of numbers that will meet two specific

conditions: In order to do this, I am going to write out as many pairs of numbers I can that will give me the product ac and then from this list, find the pair of numbers that will give me a sum equal to b.

STEP5: Rewrite the middle term of the trinomial using the two terms you found so that you have a 4 Term Polynomial

STEP6: Factor this four term polynomial using the GROUPING technique

PULL THIS PAGE FROM YOUR NOTES SO YOU CAN USE IT AS A GUIDE!

2 Terms

• After you factor out the GCF, polynomials with 2 terms factor one of three ways– Difference of squares– Difference of cubes– Sum of cubes

Difference of Squares

Meaning: A perfect square minus a perfect square

Form: F2 – L2

Factors as: (F + L)(F – L)

Examples: x2 – 9 = x2 – 32=(x + 3)(x – 3)

y2 – 36 = y2 – 62=(y + 6)(y – 6)

Difference of Cubes

Meaning: A perfect cube minus a perfect cube

Form: F3 – L3

Factors as: (F - L)(F2 + FL + L2)

Examples:

x3 – 8 =

x3 – 64 =

Sum of Cubes

Meaning: A perfect cube plus a perfect cube

Form: F3 + L3

Factors as: (F + L)(F2 - FL + L2)

Examples:

x3 + 8 =

x3 + 64 =

Sum of Squares

Meaning: A perfect square plus a perfect square

Form: F2 + L2

Factors as: DOES NOT FACTOR … do not be tempted!

Examples: x2 + 4

x2 + 100

The KEY to these are knowing what perfect squares and cubes

are

PERFECT SQUARES PERFECT CUBES

1 36

4 49

9 64

16 81

25 100 etc

1

8

27

64

125 etc

Four Terms

Factor out GCF FIRST Split the polynomial into 2 groups Factor out the GCF in the left group Factor out the GCF in the right group Look at the two groups and factor out the

common factor from both Write the remainder as the 2nd factor

Four Terms

Factor out GCF FIRST

In this example there is not one!

ab ac db dc

Four Terms

Factor out GCF FIRST

Split the polynomial into 2 groups

Yes … it really is that simple!

Four Terms

Factor out GCF FIRST Split the polynomial into 2

groups

Factor out the GCF in the left group

Factor out the GCF in the right group

Four Terms

Factor out GCF FIRST Split the polynomial into

2 groups Factor out the GCF in

the left group Factor out the GCF in

the right group Look at the two

groups and factor out the common factor from both

Four Terms

Factor out GCF FIRST Split the polynomial into 2

groups Factor out the GCF in the

left group Factor out the GCF in the

right group Look at the two groups and

factor out the common factor from both

Write the remainder as the 2nd factor

Four Terms

Factor out GCF FIRST

In this example there is not one!

3 3x y mx my

Four Terms

Factor out GCF FIRST

Split the polynomial into 2 groups

Yes … it really is that simple!

Four Terms

Factor out GCF FIRST Split the polynomial into 2

groups

Factor out the GCF in the left group

Factor out the GCF in the right group

Four Terms

Factor out GCF FIRST Split the polynomial into

2 groups Factor out the GCF in

the left group Factor out the GCF in

the right group Look at the two

groups and factor out the common factor from both

Four Terms

Factor out GCF FIRST Split the polynomial into 2

groups Factor out the GCF in the

left group Factor out the GCF in the

right group Look at the two groups and

factor out the common factor from both

Write the remainder as the 2nd factor