Differentiating Cosines with Cosines?
Calculus
Level
5
\[ \large \left[ \frac { d }{ d\left( \cos { x } \right) } \left( \sum _{ n=1 }^{ 100 }{ \cos { nx } } \right) \right] _{ { x=2\pi }} =\, ?\]
by
Swapnil Das