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By the end of this section, you will be able to:
  • Find the greatest common factor of two or more expressions
  • Factor the greatest common factor from a polynomial

Before you get started, take this readiness quiz.

  1. Factor 56 into primes.
    If you missed this problem, review Prime Factorization and the Least Common Multiple .
  2. Multiply: −3 ( 6 a + 11 ) .
    If you missed this problem, review Distributive Property .
  3. Multiply: 4 x 2 ( x 2 + 3 x 1 ) .
    If you missed this problem, review Multiply Polynomials .

Find the greatest common factor of two or more expressions

Earlier we multiplied factors together to get a product. Now, we will be reversing this process; we will start with a product and then break it down into its factors. Splitting a product into factors is called factoring.

On the left, the equation 8 times 7 equals 56 is shown. 8 and 7 are labeled factors, 56 is labeled product. On the right, the equation 2x times parentheses x plus 3 equals 2 x squared plus 6x is shown. 2x and x plus 3 are labeled factors, 2 x squared plus 6x is labeled product. There is an arrow on top pointing to the right that says “multiply” in red. There is an arrow on the bottom pointing to the left that says “factor” in red.

In The Language of Algebra we factored numbers to find the least common multiple    (LCM) of two or more numbers. Now we will factor expressions and find the greatest common factor of two or more expressions. The method we use is similar to what we used to find the LCM.

Greatest common factor

The greatest common factor    (GCF) of two or more expressions is the largest expression that is a factor of all the expressions.

First we will find the greatest common factor of two numbers.

Find the greatest common factor of 24 and 36 .

Solution

Step 1: Factor each coefficient into primes. Write all variables with exponents in expanded form. Factor 24 and 36. .
Step 2: List all factors--matching common factors in a column. .
In each column, circle the common factors. Circle the 2, 2, and 3 that are shared by both numbers. .
Step 3: Bring down the common factors that all expressions share. Bring down the 2, 2, 3 and then multiply.
Step 4: Multiply the factors. The GCF of 24 and 36 is 12.

Notice that since the GCF is a factor of both numbers, 24 and 36 can be written as multiples of 12 .

24 = 12 · 2 36 = 12 · 3
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Find the greatest common factor: 54 , 36 .

18

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Find the greatest common factor: 48 , 80 .

16

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In the previous example, we found the greatest common factor of constants. The greatest common factor of an algebraic expression can contain variables raised to powers along with coefficients. We summarize the steps we use to find the greatest common factor    .

Find the greatest common factor.

  1. Factor each coefficient into primes. Write all variables with exponents in expanded form.
  2. List all factors—matching common factors in a column. In each column, circle the common factors.
  3. Bring down the common factors that all expressions share.
  4. Multiply the factors.

Find the greatest common factor of 5 x and 15 .

Solution

Factor each number into primes.
Circle the common factors in each column.
Bring down the common factors.
.
The GCF of 5x and 15 is 5.
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Find the greatest common factor: 7 y , 14 .

7

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Find the greatest common factor: 22 , 11 m .

11

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In the examples so far, the greatest common factor was a constant. In the next two examples we will get variables in the greatest common factor.

Find the greatest common factor of 12 x 2 and 18 x 3 .

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 12 x 2 and 18 x 3 is 6 x 2
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Questions & Answers

can someone help me with some logarithmic and exponential equations.
Jeffrey Reply
sure. what is your question?
ninjadapaul
20/(×-6^2)
Salomon
okay, so you have 6 raised to the power of 2. what is that part of your answer
ninjadapaul
I don't understand what the A with approx sign and the boxed x mean
ninjadapaul
it think it's written 20/(X-6)^2 so it's 20 divided by X-6 squared
Salomon
I'm not sure why it wrote it the other way
Salomon
I got X =-6
Salomon
ok. so take the square root of both sides, now you have plus or minus the square root of 20= x-6
ninjadapaul
oops. ignore that.
ninjadapaul
so you not have an equal sign anywhere in the original equation?
ninjadapaul
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algebra 2 Inequalities:If equation 2 = 0 it is an open set?
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or infinite solutions?
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The answer is neither. The function, 2 = 0 cannot exist. Hence, the function is undefined.
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Kristine 2*2*2=8
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No. 7x -4y is simplified from 4x + (3y + 3x) -7y
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J, combine like terms 7x-4y
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Yes, Nanotechnology has a very fast field of applications and their is always something new to do with it...
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In this morden time nanotechnology used in many field . 1-Electronics-manufacturad IC ,RAM,MRAM,solar panel etc 2-Helth and Medical-Nanomedicine,Drug Dilivery for cancer treatment etc 3- Atomobile -MEMS, Coating on car etc. and may other field for details you can check at Google
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At high concentrations (>0.01 M), the relation between absorptivity coefficient and absorbance is no longer linear. This is due to the electrostatic interactions between the quantum dots in close proximity. If the concentration of the solution is high, another effect that is seen is the scattering of light from the large number of quantum dots. This assumption only works at low concentrations of the analyte. Presence of stray light.
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Need to simplify the expresin. 3/7 (x+y)-1/7 (x-1)=
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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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