Factor this quadratic expression:
a2 - 2a - 15

A² - 2a - 15
= a² - 5a + 3a - 15
= a(a-5) + 3(a-5)
= (a-5)(a+3)

A^2-2a-15

1. Ask: Which two numbers add up to -2 and multiply to -15?
-5 and 3

2. Rewrite the expression using the above
(a-5)(a+3)

Have a nice day :D