Question

If f(x) = x + 4 and g(x)=x²-1, what is (gof)(x)?

(gof)(x)=x²-1
(gof)(x)=x² +8x+16
(gof)(x)=x²+8x+15
(gof)(x)=x²+3

Answer 1

(g ￮ f)(x) = x² + 8x + 15

Explanation:

to find (g ￮ f)(x) substitute x = f(x) into g(x)

(g ￮ f)(x)

= g(f(x))

= g(x + 4)

= (x + 4)² - 1 ← expand factor using FOIL

= x² + 8x + 16 - 1 ← collect like terms

= x² + 8x + 15