Function with exponent imaginary power

Question

If we have $u=\frac{4c(e^{-is}-e^{is})}{(e^{-is}+e^{is})^2} \tag 1$

where c is a constant and s is a variable. Can we write $e^{is}$ in terms of u ? Means Can we write $e^{is}$ as $\psi(u)$ , a function of u only, from the given definition?

Answer 1

I think this can help you:

If you have other problem ask it.

Answer 2

Hint

What about using $$e^{is}=\cos(s)+i\sin(s)$$ $$e^{-is}=\cos(s)-i\sin(s)$$ I am sure that you can take from here.