Question

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Answer 1

$cosa=-\frac{3}{5}\; \; \; a\in III\; => sina<0,\; \; tga>0\\\\\\sina=-\sqrt{1-cos^2a}=-\sqrt{1-(-\frac{3}{5})^2}=-\sqrt{1-\frac{9}{25}}=-\sqrt{\frac{16}{25}}=-\frac{4}{5}\\\\\\tg=\frac{sina}{cosa}=\frac{-\frac{4}{5}}{-\frac{3}{5}}=\frac{4}{3}$