Question

How can I solve this problem?

Answer 1

(f+g)(x)=0
f (x) + g (x)=0

now,
substitute their values

x^2 -4x + x -18 = 0
x^2 -3x -18 =0
x^2 - 6x + 3x - 18 =0
x (x-6) + 3 (x-6) = 0
(x-6)(x+3) = 0


we have to find it's zeroes (or roots) now:

x-6 =0
x = 6


x +3 =0
x = -3