Power Series Expansion for Tangent Function/Proof 1

Proof
From Power Series Expansion for Cotangent Function:
 * $(1): \quad \cot x = \displaystyle \sum_{n \mathop = 0}^\infty \frac {\left({- 1}\right)^n 2^{2 n} B_{2 n} \, x^{2 n - 1} } {\left({2 n}\right)!}$

Then: