Diketahui f(x)=3x-6 dan g(x)=2x+k . jika (f • g) (x) =(g • f) (x), maka k =

f(g(x)) = g(f(x))
3(g(x)) - 6 = 2(f(x)) + k
3(2x + k) - 6 = 2(3x - 6) + k
6x + 3k - 6 = 6x - 12 + k
6x - 6x - 6 + 12 = k - 3k
6 = - 2k
k = 6/-2
k = -3