jika g(x) = x2 - 1 dan fungsi (f 0 g)(x) = x4 maka f(4) =

g(x) = x^2 - 1
(f o g)(x) = x^4
f(g(x)) = x^4

Permisalan :
x^2 - 1 = a ..... (1)
x^2 = a + 1
x = √(a + 1) ...... (2)

f(g(x)) = x^4
f(x^2 - 1) = x^4
f(a) = (√(a + 1))^4
f(a) = (√(a +1))^2 x (√(a +1))^2
f(a) = (a + 1)( a + 1)
f(x) = (x + 1)(x + 1)

Bukti :
f( g(x)) = f(x^2 - 1)
= (x^2 - 1 + 1)(x^2 - 1 +1)
= x^2 . x^2
= x^4

f(4)
= (4 + 1)(4 + 1)
= 5(5)
= 25

Jadi , f(4) = 25