Diketahui f (x)= 3x -10 dan g (x) = -4x -a. Bila (fog) (x) = (gof) (x) , hitung nilai a !

f(x) = 3x - 10
g(x) = -4x - a

(fog)(x) = (gof)(x)
f(-4x - a) = g(3x - 10)
3(-4x - a) - 10 = -4(3x -10) - a
-12x - 3a - 10 = -12x + 40 -a
-3a - 10 = 40 - a
-10 - 40 = -a + 3a
2a = -50
a = -50/2
a = -25