tolong dong pake jalan yah

5. (fog)(a)=6(5x+4)-3=81
                =30x+21=81
                =x=81-21/30
                =x=2 (D)

4) (g o f)(x) = g(f(x))
= g(√(x^2 - 1))
= 3(√(x^2 - 1))^2 - 1
= 3(x^2 - 1) - 1
= 3x^2 - 3 - 1
= 3x^2 - 4

5) (f o g)(a) = 81
f(g(a)) = 81
6g(a) - 3 = 81
6g(a) = 84
g(a) = 14
5a + 4 = 14
5a = 10
a = 2

6) (f o g)(x) = f(g(x))
= (g(x) + 4)/(g(x) - 6)
= (2x - 1 + 4)/(2x - 1 - 6)
= (2x + 3)/(2x - 7)
(2x + 3)/(2x - 7) = y
2xy - 7y = 2x + 3
2xy - 2x = 7y + 3
x(2y - 2) = 7y + 3
x = (7y + 3)/(2y - 2)
(f o g)^-1(x) = (7x + 3)/(2x - 2) ; x ≠ 1