caranya gimana master

(fog)(x) = 4x² + 4x
f(2x+1) = 4x² + 4x
misal 2x+1 = y     -----> 2x = y -1    -----> x = (y-1)/2
f(y) = 4((y-1)/2)² + 4(y-1)/2 = 4(y²-2y+1)/4 + 2y-2 = y²-1
f(x) = x² - 1