Jika f(x) = 2x + 3 dan g(x) = 9 - x, nilai dari (f o g)-1(-9) = ….
Jawab:
f(x) = 2x + 3 dan g(x) = 9 – x
Pertama-tama kita cari (f o g)(x):
(f o g)(x) = f(9 – x)
= 2(9 – x) + 3
(f o g)(x) = 21 – 2x
Selanjutnya kita cari inversnya:
y = 21 – 2x
⇔ 2x = 21 – y
⇔ x = ½ (21 – y)
⇔ (f o g)-1(x) = ½ (21 – x)
Sehingga (f o g)-1(-9) = ½ (21 – (-9)) = ½ × 30 = 15