todo
$\tan(x):=\dfrac{\sin(x)}{\cos(x)}$
$\tan(x)=\sum_{n=1}^\infty (-1)^{n-1}\frac{2^{2n} (2^{2n}-1)}{(2n)!}B_{2n}\,x^{2n-1}$
with $B_k$ … Bernoulli numbers
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| $\left(\dfrac{\tan(x)}{x}\right)^m=1+m\dfrac{1}{3}x^2+m\left(\dfrac{m}{18}+\dfrac{7}{90}\right)x^4+{\mathcal O}(x^6)$ |
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Wikipedia: Trigonometric_functions#tangent