Partial Fractions Expansion of Cotangent/Proof 1

Proof
We have that:
 * $\cot \pi x = \dfrac {\cos \pi x} {\sin \pi x}$

has a denominator which is $0$ at $x = 0, \pm 1, \pm 2, \ldots$.

Hence the limitation on the domain of $x \cot \pi x$ to exclude integer $x$.

Having established that, we should be able to express $\cot \pi x$ in the form:
 * $\cot \pi x = \dfrac a x + \displaystyle \sum_{n \mathop = 1}^\infty \left({\frac {b_n} {x - n} + \frac {c_n} {x + n} }\right)$

using a partial fractions expansion.

By evaluating the coefficients $b_n$ and $c_n$ in the usual manner, they are found to be:


 * $\forall n \in \N: b_n = c_n = \dfrac 1 \pi$

The result follows.