Найдите tga, если sina= -4/5, 180 ≤ а ≤ 270

[latex]sina=-\frac{4}{5}\\\\180^\circ \ \textless \ a\ \textless \ 270^\circ \; \; \; \Rightarrow \quad tga\ \textgreater \ 0\; ,\; \; cosa\ \textless \ 0\\\\cosa=-\sqrt{1-sin^2a}=-\sqrt{1- \frac{16}{25} }=-\sqrt{\frac{9}{25}}=- \frac{3}{5} \\\\tga=\frac{sina}{cosa}= \frac{-4/5}{-3/5} = \frac{4}{3} [/latex]