0.3 Factoring Polynomials

0.3 Factoring Polynomials
Unit 0 Review of Basic Concepts

Concepts and Objectives
 Factoring out the greatest common factor
 Factoring by Grouping
 Factoring Trinomials
 Factoring by Substitution

Factoring Polynomials
 The process of finding polynomials whose product
equals a given polynomial is called factoring.
 For example, since 4x + 12 = 4(x + 3), both 4 and x + 3
are called factors of 4x + 12.
 A polynomial that cannot be written as a product of two
polynomials of lower degree is a prime polynomial.
 One nice aspect of this process is that it has a built-in
check: whatever factors you come up with, you should
be able to multiply them and get your starting
expression.

Factoring Out the GCF
Factor out the greatest common factor from each
polynomial:



5 2
9y y
2
6 8 12x t xt t 
     3 2
14 1 28 1 7 1m m m    

Factoring Out the GCF
Factor out the greatest common factor from each
polynomial:
 GCF: y2
 GCF: 2t

GCF: 7m + 1
5 2
9y y
2
6 8 12x t xt t 
     3 2
14 1 28 1 7 1m m m    
 32
9 1y y 
 2
62 3 4xt x 
     2
47 1 2 1 1 1m mm     
 

Factoring Out the GCF (cont.)
We can clean up that last problem just a little more:
     
     
 
  
2
2
2
2
3
7 2 1 4 1 1
7 1 2 2 1 4 1 1
7 1 2 4 2 4 4
1
1
7 1 2
m m
m m m m
m m m
m m
m
m
    
 
       
     


 


Factoring by Grouping
 When a polynomial has more than three terms, it can
sometimes be factored using factoring by grouping. For
example, to factor
ax + ay + 6x + 6y,
group the terms so that each group has a common factor.
   
   
  
6 6 6 6
6
6
ax ay x y ax ay x y
a x y x y
x y a
      
   
  
x + y is the GCF
of the expression
above.

Factoring by Grouping (cont.)
Examples: Factor each polynomial by grouping.


2 2
7 3 21mp m p  
2 2
2 2y az z ay  



   
  
2 2 2 2
2
7 3 21 7 3 7
7 3
mp m p m p p
p m
      
  
2 2
2 2y az z ay  



   
  
2 2 2 2
2
7 3 21 7 3 7
7 3
mp m p m p p
p m
      
  
   
   
  
2 2 2 2
2 2
2 2
2
2 2 2 2
2 2
2
2
y az z ay y z az ay
y z ay az
y z a y z
y z a
      
    
   
  

 3 2
4 2 2 1x x x  

    
   
  
3 2 3 2
2
2
4 2 2 1 4 2 2 1
2 2 1 1 2 1
2 1 2 1
x x x x x x
x x x
x x


    
 
 




Perfect Square Trinomials
 We can use the reverse of the special patterns we saw
last class to quickly factor perfect square trinomials if
we can recognize the pattern.
 If you encounter a trinomial which fits this pattern, you
can quickly factor it by taking the square roots of the
first and last term.
 22 2
2a ab b a b   

 Example: Factor 9x2 ‒ 12x + 4

 Example: Factor 9x2 ‒ 12x + 4
The first thing to notice is that the first and last terms
are perfect squares, and that the middle term is two
times the product of the square roots.
To factor this, put the two square roots together, along
with whatever the sign is between the first and second
term.
2
9 3 and 4 2x x    2 3 4 12x x
 22
9 12 4 3 2x x x  

Examples: Factor the following



2 2
16 40 25p pq q 
2 2
36 84 49x y xy 
2
81 90 25a a 

Examples: Factor the following



      
 
2 22 2
2
16 40 25 4 2 4 5 5
4 5
p pq q p p q q
p q
    
 
    
 
22 2 2
2
36 84 49 6 2 6 7 7
6 7
x y xy xy xy
xy
    
 
    
 
22 2
2
81 90 25 9 2 9 5 5
9 5
a a a a
a
    
 

Factoring Trinomials
If you have an expression of the form ax2 +bx + c, you can
use one of the following methods to factor it:
 X-method (a = 1): If a = 1, this is the simplest method to
use. Find two numbers that multiply to c and add up to
b. These two numbers will create your factors.
 Example: Factor x2 ‒ 5x ‒ 14.
‒14
‒7 2
‒5
  2
5 14 7 2x x x x    

Factoring Trinomials (cont.)
 Reverse box: If a is greater than 1, you can use the
previous X method to split the middle term (ac goes on
top) and the box method, and then find the GCF of each
column and row.
 Example: Factor
Now, find the GCF of each line.
 2
4 5 6y y
‒24
‒8 3
5
4y2 ‒8y
3y ‒6

 Reverse box: If a is greater than 1, you can use the
previous X method to split the middle term (ac goes on
top) and the box method and find the GCF of each
column and row.
 Example: Factor  2
4 5 6y y
‒24
‒8 3
5
y ‒2
4y 4y2 ‒8y
3 3y ‒6
      2
4 5 6 4 3 2y y y y

 Grouping: This method is about the same as the Reverse
Box, except that it is not in a graphic format.
 Example: Factor 2
2 6x x 
‒12
‒4 3
‒1
   
   
  
2 2
2
2 6 2 6
2 4 3 6
2 2 3 2
2 2 3
4 3x x x
x x x
x x
x
x
x
x x
   
   





  


Factoring Binomials
 If you are asked to factor a binomial (2 terms), check
first for common factors, then check to see if it fits one of
the following patterns:
 Note: There is no factoring pattern for a sum of
squares (a2 + b2) in the real number system.
Difference of Squares a2 ‒ b2 = a + ba ‒ b
Sum/Diff. of Cubes   3 3 2 2
a b a b a ab b   

Factoring Binomials (cont.)
Examples
 Factor
 Factor
 Factor
2
4 81x 
3
27x 
3
3 24x 
 
  
2 2
2 9
2 9 2 9
x
x x
 
  
  
3 3
2
3
3 3 9
x
x x x



  
   
  
3 3 3
2
3 8 3 2
3 2 2 4
x x
x x x
   
   

Factoring Binomials (cont.)
EVERY TIME YOU DO THIS:
A KITTEN DIES
 2 2 2
x y x y  
Remember:

Classwork
 College Algebra (evens unless otherwise noted)
 Page 40: 2-24, pg. 30: 44-58, 0.1 WS #2 (all)

0.3 Factoring Polynomials

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