How do you factor the trinomial #a^2 - 4a - 21#?

1 Answer
Wayne
Mar 30, 2016

#(a+3)(a-7)#

Explanation:

For a trinomial of this type we can factor it by looking for two numbers which multiply together to equal #-21# and have a sum of#-3#

In this case: #(+3)#and #(-7)# meet tis requirement.

#(+3)(-7)=-21#

#(+3)+(-7)=-4#

Using this information I can factor #a^2-4a-21# into:

#(a+3)(a-7)#

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