Diketahui fungsi f dan fungsi g pada R dengan g(x) = x-9. Tentukan rumus fungsi f(x), jika:

g(x) = x – 9

a]

(g○f)(x) = g(f(x))

5x – 3 = f(x) – 9

f(x) = 5x – 3 + 9

f(x) = 5x + 6

b]

(f○g)(x) = f(g(x))

x^2 – 16x = f(x – 9)

misalkan :

t = x – 9 sehingga x = t + 9

f(x – 9) = x^2 – 16x

f(t) = (t + 9)^2 – 16(t + 9)

f(t) = t^2 + 18t + 81 – 16t – 144

f(t) = t^2 + 2t – 63

f(x) = x^2 + 2x – 63