Question

Factor completely and then place the factors in the proper location.
a 2 - a - 20?

Answer 1

Answer: (a-5)(a+4)

Explanation:

Answer 2

This is a notable trinomial.

You have to find two numbers which summed give 1 and multiplied give 20.

In this case +4 and -5

-5+4 = -1(a)

-5*4 = -20

So (a+4)(a-5)