Jika g(x)=x²-1 Dan fungsi memenuhi (f. g) (x) =x²,maka f(4)

(f o g) (x) = x²
f(g(x)) = x²
f(x² - 1) = x²
misal x² - 1 = p maka x² = p + 1
f(p) = (p + 1)²
f(p) = p² + 2p + 1
f(x) = x² + 2x + 1

f(4) = (4)² + 2(4) + 1
f(4) = 16 + 8 + 1
f(4) = 25

maka nilai f(4) = 25