Question

factor. x^2+7x-18

Answer 1

when you factor you break the original equation into 2 parts which multiply to give the original

since the original has x^2 in it the factors must be
(x+a) and (x+b)

so we can write

x^2+7x-18 = (x+a)(x+b)

do you follow so far?

Answer 2

BUT we can expand the right side so that it is

x^2 + x(a+b) + ab