Підготовка до ЗНО з математики. Алгебра.

$\begin{array}{l}\sin \alpha = \frac{{2tg\frac{\alpha }{2}}}{{1 + t{g^2}\frac{\alpha }{2}}},\alpha \ne \pi + 2\pi n,n \in Z;\\\cos \alpha = \frac{{1 - t{g^2}\frac{\alpha }{2}}}{{1 + t{g^2}\frac{\alpha }{2}}},\alpha \ne \pi + 2\pi n,n \in Z;\\tg\,\alpha = \frac{{2tg\frac{\alpha }{2}}}{{1 - t{g^2}\frac{\alpha }{2}}},\alpha \ne \frac{\pi }{2} + \pi n,\alpha \ne \pi + 2\pi n,n \in Z;\\\sin \alpha = \frac{{2tg\frac{\alpha }{2}}}{{2tg\frac{\alpha }{2}}},\alpha \ne \pi n,n \in Z.\end{array}$