Diketahui f(x)=3x-6 dan g(x)=2x+a.jika (f.g)(x)=(g.f)(x). Tentukan nilai a

Mungkin seharusnya soalnya "Jika (fog)(x) = (gof)(x)..."

(fog)(x) = f(g(x))
             = 3(2x + a) - 6
             = 6x + 3a - 6

(gof)(x) = g(f(x))
             = 2(3x - 6) + a
             = 6x - 12 + a

(fog)(x) = (gof)(x)
6x + 3a - 6 = 6x - 12 + a
6x - 6x + 3a - a = - 12 + 6
2a = - 6
a = (- 6) / (2)

a = - 3