1. § 5.3
Greatest Common Factors and Factoring by Grouping

2. Factoring
Factoring a polynomial means finding an equivalent expression that is a product. For example, when we take the polynomial
And write it as
we say that we have factored the polynomial. In factoring, we write a
sum as a product.
Blitzer, Intermediate Algebra, 5e – Slide #2 Section 5.3

3. Factoring a Monomial from a Polynomial
1) Determine the greatest common factor of all terms in the polynomial.
2) Express each term as the product of the GCF and its other factor.
3) Use the distributive property to factor out the GCF.
Blitzer, Intermediate Algebra, 5e – Slide #3 Section 5.3

4. Factoring
EXAMPLE
Factor:
SOLUTION
First, we determine the greatest common factor of the three terms.
Notice that the greatest integer that divides into 49, 70 and 35 (the coefficients of the terms) is 7. The variables raised to the smallest exponents are
The GCF is
Blitzer, Intermediate Algebra, 5e – Slide #4 Section 5.3

5. Factoring
CONTINUED
Express each term as the product of the GCF and its other factor
Factor out the GCF
Blitzer, Intermediate Algebra, 5e – Slide #5 Section 5.3

6. Factoring
EXAMPLE
Factor:
SOLUTION
The GCF is 5x. Because the leading coefficient, -5, is negative, we factor out a common factor with a negative coefficient. We will factor out the negative of the GCF, or -5x.
Express each term as the product of the GCF and its other factor
Factor out the GCF
Blitzer, Intermediate Algebra, 5e – Slide #6 Section 5.3

7. Factoring by Grouping Factor:
EXAMPLE
Factor:
SOLUTION
Let’s identify the common binomial factor in each part of the problem.
The GCF, a binomial, is x + y.
The GCF, a binomial, is x + y.
Blitzer, Intermediate Algebra, 5e – Slide #7 Section 5.3

8. Factoring by Grouping
CONTINUED
We factor out the common binomial factor as follows.
This step, usually omitted, shows each term as the product of the GCF and its other factor, in that order.
Factor out the GCF
Blitzer, Intermediate Algebra, 5e – Slide #8 Section 5.3

9. Factoring by Grouping Factoring by Grouping
1) Group terms that have a common monomial factor. There will usually be two groups. Sometimes the terms must be rearranged.
2) Factor out the common monomial factor from each group.
3) Factor out the remaining common binomial factor (if one exists).
Blitzer, Intermediate Algebra, 5e – Slide #9 Section 5.3

10. Factoring by Grouping Factor:
EXAMPLE
Factor:
SOLUTION
There is no factor other than 1 common to all terms. However, we can group terms that have a common factor: +
Common factor is :
Use -2b, rather than 2b, as the common factor: -2bx – 4by = -2b(x + 2y). In this way, the common binomial factor, x + 2y, appears.
Blitzer, Intermediate Algebra, 5e – Slide #10 Section 5.3

11. Factoring by Grouping
CONTINUED
The voice balloons illustrate that it is sometimes necessary to use a factor with a negative coefficient to obtain a common binomial factor for the two groupings. We now factor the given polynomial as follows:
Group terms with common factors
Factor out the common factors from the grouped terms
Factor out the GCF
Blitzer, Intermediate Algebra, 5e – Slide #11 Section 5.3

12. Factoring by Grouping
EXAMPLE
Your local electronics store is having an end-of-the-year sale. The price on a large-screen television had been reduced by 30%. Now the sale price is reduced by another 30%. If x is the television’s original price, the sale price can be represented by
(x – 0.3x) – 0.3(x – 0.3x)
Factor out (x – 0.3x) from each term. Then simplify the resulting expression.
Use the simplified expression from part (a) to answer these questions. With a 30% reduction followed by a 30% reduction, is the television selling at 40% of its original price? If not, at what percentage of the original price is it selling?
Blitzer, Intermediate Algebra, 5e – Slide #12 Section 5.3

13. Factoring by Grouping (a) (x – 0.3x) – 0.3(x – 0.3x)
CONTINUED
SOLUTION
(a) (x – 0.3x) – 0.3(x – 0.3x)
= 1(x – 0.3x) – 0.3(x – 0.3x)
This step, usually omitted, shows each term as the product of the GCF and its other factor, in that order.
= (x – 0.3x)(1 – 0.3)
Factor out the GCF
= (x – 0.3x)(0.7)
Subtract
= 0.7x – 0.21x
Distribute
= 0.49x
Subtract
Blitzer, Intermediate Algebra, 5e – Slide #13 Section 5.3

14. Factoring by Grouping
CONTINUED
(b) With a 30% reduction, followed by another 30% reduction, the expression that represents the reduced price of the television simplifies to 0.49x. Therefore, this series of price reductions effectively gives a new price for the television at 49% its original price, not 40%.
Blitzer, Intermediate Algebra, 5e – Slide #14 Section 5.3