How to Factor Out the Greatest Common Factor

The greatest common factor (GCF) is the largest possible term that evenly divides each term of an expression containing two or more terms. The most common and easiest factoring method is GCF, and it’s helpful when solving equations. In an expression with two or more terms, finding the greatest common factor can make the expression more understandable and manageable.

The best case scenario is to recognize and pull out the GCF from a list of terms. Sometimes, though, the GCF may not be so recognizable. These steps help you find it, using this expression 12x2y4 + 16xy3 – 20x3y2 as an example:

  1. Determine any common numerical factors.

    Each term has a coefficient that is divisible by a power of 2, which is 4.

  2. Determine any common variable factors.

    Each term has x and y factors. The prime factorizations should help to show what the GCF is.

  3. Write the prime factorizations of each term.

    12x2y4 = 22 × 3 × x2y4

    16xy3 = 24 × xy3

    –20x3y2 = – 22 × 5 × x3y2

    The GCF is the product of all the factors that all three terms have in common.

  4. Find the GCF.

    The GCF contains the lowest power of each variable and number that occurs in any of the terms. Each variable in the sample problem has a factor of 2. If the lowest power of 2 that shows in any of the factors is 22, then 22 is part of the GCF.

    When finding the greatest common factor (GCF) of terms, the lowest power (exponent) of a particular factor that occurs in any of the terms determines the power of that factor in the GCF.

    Each factor has a power of x. If the lowest power of x that shows up in any of the factors is 1, then x1 is part of the GCF.

    Each factor has a power of y. If the lowest power of y that shows in any of the factors is 2, then y2 is part of the GCF.

    The GCF is 22xy2 = 4xy2.

  5. Divide each term by the GCF.

    The respective terms are divided as shown:

    image0.png image1.png image2.png

    Notice that all three results of the division have nothing in common. The first two terms each have a y, and the first and third each have an x, but nothing is shared by all the results. This is the best factoring result, which is what you want.

  6. Rewrite the original expression with the GCF factored out and in parentheses:

    12x2y4 + 16xy3 – 20x3y2 = 4xy2 (3xy2 + 4y –5x2)

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