How do you factor the trinomial a^2 - 4a - 21a24a21?

1 Answer
Mar 30, 2016

(a+3)(a-7)(a+3)(a7)

Explanation:

For a trinomial of this type we can factor it by looking for two numbers which multiply together to equal -2121 and have a sum of-33

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

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

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

Using this information I can factor a^2-4a-21a24a21 into:

(a+3)(a-7)(a+3)(a7)