I am trying to check if this assertion is true, though i am bit rusty with integration and little unsure how to solve this integral.
Is the following statement true: $\int_0^{2\pi} \cos(k \theta) \cos(j \theta) d \theta = 0$ if $j \neq k$ and $j, k \geq 1$ are integers.
Any pointers of hints would be much appreciated.