why is this question spining my head?

Question

could u pls approximate f(y) given
f(f(y))=g(y)? i.e., if f(f(y))=y^4, then f(y)=y^2?
what method could be used to approximate to f(f(y))=e^y.

Answer 1

Uh, your head is spinning because you're Lucifer's cousin?

Answer 2

You need to ask this question in the Math Section. Although there are people here who could answer it (not me, I only took Cal 2), it is not the appropriate forum for it.