Question

How do you factor completely `3a^2+12a-15`?

Answer 1

(x - 1)(3x + 15)

Explanation:

`y = 3a^2 + 12a - 15`
Since a + b + c = 0, use shortcut.
One real root is x = 1 and the factor is (x - 1)
One real roots is `c/a = -15/3`, and the factor is `(x + 15/3)`
`y = (x -1)(x + 15/3) = (x - 1)(3x + 15)`