Let $(X,M,\mu)$ be a finite measure space and let $f$ be a real-valued and measurable function on $X$. How do I evaluate $$ \lim_{n\rightarrow \infty} \int_X ~{\left\{\cos\left(\pi f(x)\right) \right\}}^{2n}~\text{d}\mu(x)$$ in terms of $f$?
Thanks for helping.