F(x) = 2x + b dan f^(9) =3, maka nilai f(f(3))

f(x)=y=2x+b
y+b=2x
x=(y+b)/2
f^-1(x)=(x+b)/2
f^-1(9)=3
3+b/2=3
3+b=2.3
3+b=6
b=6-3
b=3
f(f(3))=f(2(3)+3)
= f(6+3)
= f(9)
=2(9)+3
=18+3
=21

maaf kalau salah

f(x) = 2x + b
f^-1(9) = 3 => f(3) = 9
=> 2(3) + b = 9
=> 6 + b = 9
=> b = 3
Jadi f(x) = 2x + 3
f(f(3)) = f(9) = 2(9) + 3 = 21