Diketahui fungsi f (x)=2-x dan g(x)=2x+a+1. jika (fog)(x)=(gof)(x), maka nilai dari a adalah

F(x) = 2 – x
g(x) = 2x + a + 1
(fog)(x) = f(g(x)) = 2 – (2x + a + 1)
(fog)(x) = -2x – a +1
(gof)(x) = g(f(x)) = 2(2 – x) + a +1
(gof)(x) = -2x + a + 5
(fog)(x) = (gof)(x)
-2x – a +1 = -2x + a + 5
-2a = 4
a = -2
Jadi a = -2

Ok?