Diketahui: f(x)= 3x^2 – 4x + 5 g(x)= 2x + 7 ditanya. : a. (gof) (-1) b. (fog) (2)

diketahui: f(x)= 3x^2 – 4x + 5
g(x)= 2x + 7
ditanya. : a. (gof) (-1)
b. (fog) (2)

Jawaban:
(g o f)(-1) = 31
(f o g)(2) = 324

perhatikan konse fungsi komposisi berikut:
(f o g)(x) = f(g(x))
(g o f)(x) = g(f(x))

Diketahui:
f(x) = 3x^2 – 4x + 5
g(x) = 2x + 7

Ditanya:
a. (g o f)(-1) = … ?
b. (fog)(2) = … ?

Pembahasan:
a. (g o f)(-1) = … ?
(g o f)(x) = g(f(x))
(g o f)(x) = 2(f(x)) + 7
(g o f)(x) = 2(3x^2 – 4x + 5) + 7
(g o f)(-1) = 2(3(-1)^2 – 4(-1) + 5) + 7
(g o f)(-1) = 2(3(1) – (-4) + 5) + 7
(g o f)(-1) = 2(3 + 4 + 5) + 7
(g o f)(-1) = 2(12) + 7
(g o f)(-1) = 24 + 7
(g o f)(-1) = 31

b. (fog)(2) = … ?
(f o g)(x) = f(g(x))
(f o g)(x) = 3(g(x))^2 – 4(g(x)) + 5
(f o g)(x) = 3(2x + 7)^2 – 4(2x + 7) + 5
(f o g)(2) = 3(2(2) + 7)^2 – 4(2(2) + 7) + 5
(f o g)(2) = 3(4 + 7)^2 – 4(4 + 7) + 5
(f o g)(2) = 3(11)^2 – 4(11) + 5
(f o g)(2) = 3(121) – 4(11) + 5
(f o g)(2) = 363 – 44 + 5
(f o g)(2) = 319 + 5
(f o g)(2) = 324

Jadi, hasilnya adalah
(g o f)(-1) = 31
(f o g)(2) = 324