tolong bantu jawab dengan menggunakan dengan cara!!

f(x) = 5x² + 1
g(x) = 1/x +1

f o g (a) = 21

Ditanya : nilai a??

Jawaban :

f o g (x) = f(g(x)) = f(1/x + 1)
f o g (x) = 5(1/x + 1)² + 1

Maka
f o g (a) = 21
5(1/x + 1)² + 1 = 21
5(1/x + 1)² = 21 -1
(1/x + 1)² = 20/5
(1/x + 1)² = 4
1/x + 1 = √4
1/x + 1 = 2
1/x = 2-1
1/x = 1
x = 1

Jadi nilai a = 1