Diketahui fungsi f(x)= x^, x>0 dan g(x)= 5x1 jika ( f o g ) invers (a)=2. Tentukan nilai a

jawab
fungsi 
f(x) = x²
g(x) = 5x + 1

fog(x) = f {g(x)} 
fog(x) = f (5x + 1)
fog(x)= (5x +1)²

(fog)⁻¹(a)= 2 
fog(2)=  a
(5.2 +1)² = a
(10 +1)² = a
a= 11²
a = 121