Hello, i need find partial sum and verify convergence of this sequence. I have idea to apply euler formula. Early i solved similiar problem but this square, i dont know. \begin{equation}
\sum_{n=1}^{\infty} \cos ^{2}(n x)
\end{equation}
Help please
\sum_{n=1}^{\infty} \cos ^{2}(n x)
\end{equation}
Help please