Question

Factorise: a^2 + 8a - 20

Answer 1

Which two numbers add up to 88 and multiply to −20?
−2 and 10

Rewrite the expression using the above:

Answer:
(a−2)(a+10)

Answer 2

You would use the quadratic formula or graph it to find your factors. Your factors are: 

(x+10)(x-2)