Срочно эти два примера.

Решите задачу:

$3)\; \; sina= \frac{5}{13}\; ,\; \; tga=?\\\\0^\circ \leq a\ \textless \ 90^\circ \quad \Rightarrow \; \; \; cosa\ \textgreater \ 0\; ,\; \; tga\ \textgreater \ 0\\\\cosa=+\sqrt{1-sin^2a}=\sqrt{1-\frac{25}{169}}=\sqrt{\frac{144}{169}}= \frac{12}{13} \\\\tga= \frac{sina}{cosa}= \frac{5/13}{12/13}= \frac{5}{12} \\\\4)\; \; cosa=-\frac{8}{17}\ \textless \ 0\; \; \; \Rightarrow\; \; \; 90^\circ \ \textless \ a\ \textless \ 270^\circ \\\\sina=\pm \sqrt{1-cos^2a}=\pm \sqrt{1-\frac{64}{289}}=\pm \sqrt{ \frac{225}{289} } =\pm \frac{15}{17}\\\\ctga= \frac{cosa}{sina}=\frac{-8/17}{\pm15/17} =\pm \frac{8}{15}$

$ctga=-\frac{8}{15}\; ,\; \; esli\; \; 90^\circ \ \textless \ a\ \textless \ 180^\circ \\\\ctga=\frac{8}{15}\; ,\; \; esli\; \; 180^\circ \ \textless \ a\ \textless \ 270^\circ$