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Number Theory

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Moderate

What is $\sum_{m = 1}^{n} \cos(m\pi)$?

NUMTH-NR8WWY

Let $n \in \mathbb{N}$.

What is $\sum_{m = 1}^{n} \cos(m\pi)$?

A

$0$

B

$-1$

C

$\infty$

D

$\cfrac{\cos(n\pi) - 1}{2}$