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Find the greatest common factor: 16 x 2 , 24 x 3 .

8 x 2

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Find the greatest common factor: 27 y 3 , 18 y 4 .

9 y 3

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Find the greatest common factor of 14 x 3 , 8 x 2 , 10 x .

Solution

Factor each coefficient into primes and write
the variables with exponents in expanded form.
Circle the common factors in each column.
Bring down the common factors.
Multiply the factors.
.
The GCF of 14 x 3 and 8 x 2 , and 10 x is 2 x
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Find the greatest common factor: 21 x 3 , 9 x 2 , 15 x .

3 x

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Find the greatest common factor: 25 m 4 , 35 m 3 , 20 m 2 .

5 m 2

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Factor the greatest common factor from a polynomial

Just like in arithmetic, where it is sometimes useful to represent a number in factored form (for example, 12 as 2 · 6 or 3 · 4 ), in algebra it can be useful to represent a polynomial in factored form. One way to do this is by finding the greatest common factor of all the terms. Remember that you can multiply a polynomial by a monomial as follows:

2 ( x + 7 ) factors 2 · x + 2 · 7 2 x + 14 product

Here, we will start with a product, like 2 x + 14 , and end with its factors, 2 ( x + 7 ) . To do this we apply the Distributive Property “in reverse”.

Distributive property

If a , b , c are real numbers, then

a ( b + c ) = a b + a c and a b + a c = a ( b + c )

The form on the left is used to multiply. The form on the right is used to factor.

So how do we use the Distributive Property to factor a polynomial? We find the GCF of all the terms and write the polynomial as a product!

Factor: 2 x + 14 .

Solution

Step 1: Find the GCF of all the terms of the polynomial. Find the GCF of 2x and 14. .
Step 2: Rewrite each term as a product using the GCF. Rewrite 2x and 14 as products of their GCF, 2.
2 x = 2 x
14 = 2 7
.
Step 3: Use the Distributive Property 'in reverse' to factor the expression. 2 ( x + 7 )
Step 4: Check by multiplying the factors. Check:
.
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Factor: 4 x + 12 .

4( x + 3)

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Factor: 6 a + 24 .

6( a + 4)

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Notice that in [link] , we used the word factor as both a noun and a verb:

Noun 7 is a factor of 14 Verb factor 2 from 2 x + 14

Factor the greatest common factor from a polynomial.

  1. Find the GCF of all the terms of the polynomial.
  2. Rewrite each term as a product using the GCF.
  3. Use the Distributive Property ‘in reverse’ to factor the expression.
  4. Check by multiplying the factors.

Factor: 3 a + 3 .

Solution

.
.
Rewrite each term as a product using the GCF. .
Use the Distributive Property 'in reverse' to factor the GCF. .
Check by multiplying the factors to get the original polynomial.
.
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Factor: 9 a + 9 .

9( a + 1)

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Factor: 11 x + 11 .

11( x + 1)

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The expressions in the next example have several factors in common. Remember to write the GCF as the product of all the common factors.

Factor: 12 x 60 .

Solution

.
.
Rewrite each term as a product using the GCF. .
Factor the GCF. .
Check by multiplying the factors.
.
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Factor: 11 x 44 .

11( x − 4)

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Factor: 13 y 52 .

13( y − 4)

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Now we’ll factor the greatest common factor    from a trinomial    . We start by finding the GCF of all three terms.

Factor: 3 y 2 + 6 y + 9 .

Solution

.
.
Rewrite each term as a product using the GCF. .
Factor the GCF. .
Check by multiplying.
.
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Factor: 4 y 2 + 8 y + 12 .

4( y 2 + 2 y + 3)

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Factor: 6 x 2 + 42 x 12 .

6( x 2 + 7 x − 2)

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In the next example, we factor a variable from a binomial    .

Factor: 6 x 2 + 5 x .

Solution

6 x 2 + 5 x
Rewrite each term as a product. .
Factor the GCF. x ( 6 x + 5 )
Check by multiplying.
x ( 6 x + 5 )
x 6 x + x 5
6 x 2 + 5 x
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Practice Key Terms 1

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Source:  OpenStax, Prealgebra. OpenStax CNX. Jul 15, 2016 Download for free at http://legacy.cnx.org/content/col11756/1.9
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