If f (3sinx) = cos square X / sin square x is known, find f (x)= I'm a beginner. Please elaborate

If f (3sinx) = cos square X / sin square x is known, find f (x)= I'm a beginner. Please elaborate

F (3sinx) = cos square X / sin square x
=(1-sin square x) / sin square x
=1 / sinx-1 = 9 / (3sinx) - 1
f(x)=9/x^2-1