Cotangent Function is Odd

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Theorem

Let $x \in \R$ be a real number.

Let $\cot x$ be the cotangent of $x$.


Then, whenever $\cot x$ is defined:

$\map \cot {-x} = -\cot x$

That is, the cotangent function is odd.


Proof

\(\displaystyle \map \cot {-x}\) \(=\) \(\displaystyle \frac {\map \cos {-x} } {\map \sin {-x} }\) Cotangent is Cosine divided by Sine
\(\displaystyle \) \(=\) \(\displaystyle \frac {-\sin x} {\cos x}\) Cosine Function is Even and Sine Function is Odd
\(\displaystyle \) \(=\) \(\displaystyle -\cot x\) Cotangent is Cosine divided by Sine

$\blacksquare$


Also see


Sources