diketahui f(x) =x² - 3x, g(x) = x + 2 dan fog (x) =15. nilai x yang memenuhi adalah

f(x) = x² - 3x
g(x) = x+2
(fog)(x) = f(g(x))
(fog)(x) = (x+2)² - 3(x+2)
(fog)(x) = x²+4x+4-3x-6 
(fog)(x) = x²+x -2
karena (fog)(x) = 15:
15 = x²+x -2
x²+x -2 - 15 =0
x²+x -17 = 0
(x+1/2)²-1/4-17 = 0
(x+1/2)² - (-69)/4 = 0
(x+1/2)² = 69/4
(x+1/2) = +- √(69/4)
x1 = (-1/2) + √(69/4)
x2 = (-1/2) - √(69/4)

semoga membantu