Cosine of Half-Integer Multiple of Pi
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Theorem
Let $x \in \R$ be a real number.
Let $\cos x$ denote the cosine of $x$.
Then:
- $\forall n \in \Z: \map \cos {n + \dfrac 1 2} \pi = 0$
Proof
This is established in Zeroes of Sine and Cosine.
$\blacksquare$