$$\frac{\tan^{3}\alpha}{1+\tan^{2}\alpha}+\frac{\cot^{3}\alpha}{1+\cot^{2}\alpha}=\frac{1-2\ \sin^{2}\alpha\ \cos^{2}\alpha}{\sin\ \alpha\ \cos\ \alpha}$$
$\alpha \neq \frac{\pi n_{1}}{2}$
$\forall n_{1}\in \mathrm{Z}$
