2021-6-6 · As the title says, I need to calculate the sum of the function series $$sum_{n=1}^{infty}frac{cos^3(nx)}{n^2}$$ so that I can find out if the series does simple or uniform converge to something.. Usually, for problems like this I need to write the sum like a difference of sums so when we write the sums, some terms will go away, but I can''t think of a way to write this one.