Power Series Expansion for Tangent Function/Proof 1

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

Then: