diketahui f (x)=6x-3. g (x)=5x+4 dan (fog)(a)=81 nilai a=

Bab Fungsi Komposisi
Matematika SMA Kelas X

(fog) (x) = f(5x + 4)
(fog) (x) = 6(5x + 4) - 3
(fog) (x) = 30x + 24 - 3
(fog) (x) = 30x + 21

(fog) (a) = 81
30a + 21 = 81
30a = 81 - 21
a = 60/30
a = 2

Jawaban: [tex]a=2[/tex]

Karena [tex]\left(f\circ g\right)\left(a\right)=f\left(g\left(a\right)\right)[/tex] maka

[tex]f\left(g\left(a\right)\right) & =f\left(5a+4\right)\\ & =6\left(5a+4\right)-3\\ & =30a+24-3\\ & =30a+21[/tex]

Sehingga,

[tex]81=30a+21 \quad atau\quad a=2[/tex]