Jika : f(x) = x² - 3x + 5 g(x) = x + 2 f(g(a) = 81 = ?

f(g(a)) = 15
g(a) = a + 2
f(a+2) = 15
15 = (a+2)² - 3.(a+2) + 5
     = a² + 4a + 4 - 3a - 6 + 5
     = a² + a + 3
a² + a + 3 - 15 = 0
(a+4) (a-3) = 0
a = -1
a = 3