I need to factor the expression

Question

z^2 + 15z - 54

I think it's either (z - 9)(z + 6) OR
(z - 6)(z + 9)

Can you help me out? Thanks!

Answer 1

It's neither.

z^2 + 15z + 54 = (z+6)(z+9)
z^2 - 15z + 54 = (z-6)(z-9)

z^2 + 15z - 54 = (z+18)(z-3)