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Learn about the concept of greatest common factor in factoring equations and how to apply it using the distributive law. Practice exercises included.
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Section 3.11 Greatest Common Factors
Questions • What is the “greatest common factor”? • How do we find the greatest common factor? • How can we use the distributive law to “factor out” the greatest common factor?
Definition Factoring is the process of writing a sum or difference as a product.
Definition Factoring is the process of writing a sum or difference as a product. The most simple form of factoring is using the distributive law (backwards).
Definition Factoring is the process of writing a sum or difference as a product. The most simple form of factoring is using the distributive law (backwards). For example: 6x– 3 can be factored as 3(2x– 1).
Definition The greatest common factorof an expression is largest factor that will divide every term of the expression. Numerically: The largest number that divides each coefficient Variables: Each variable that appears in all terms raised to the lowest power that appears in any term
Factoring Out the GCF • Find the GCF of all the terms in the expression. • Write the GCF in front of a set of parentheses. • Fill in the parentheses by determining the terms that are necessary to create the original expression if the distributive law were used. Notes: • The number of terms in the original expression is the same as the number of terms inside the parentheses. • If the terms have no common factor other than 1, the expression cannot be factored using the GCF.
For Example • The GCF of 6x2y + 9xy5 is 3xy so we could factor as 3xy(2x+3y4) • The GCF of 12x2y3– 6x3y + 9x2is 3x2 so we could factor as 3x2(4y3– 2xy + 3)
Exercise 1 Factor out the GCF from each expression. (a) (b) (c)
Exercise 1 Factor out the GCF from each expression. (a) 15x(2x + 5y) (b) 7wz(2x – 4z2 + 1) (c) 4(6 – 2x + 3x3 + 4x5)
Factoring by Grouping When there are 4 or more terms that do not have a common factor to all the terms but do have common factors when considered in groups, factoring by grouping can be used. Consider:
Exercise 2 Use factor by grouping to factor the following: (a) (b)
Exercise 2 Use factor by grouping to factor the following: (a) (x + 5)(x + 9) (b) (y + 11)(x + 10)