0\; ,\; \; tga<0\\\\cosa=+\sqrt{1-sin^2a}=\sqrt{1-\frac{144}{169}}=\frac{5}{13}\\\\tga=\frac{sina}{cosa}=\frac{-12/13}{5/13}=-\frac{12}{5}" alt="sina=-\frac{12}{13}\\\\\frac{3\pi}{2}\leq a\leq 2\pi \; \; \to \; \; \; cosa>0\; ,\; \; tga<0\\\\cosa=+\sqrt{1-sin^2a}=\sqrt{1-\frac{144}{169}}=\frac{5}{13}\\\\tga=\frac{sina}{cosa}=\frac{-12/13}{5/13}=-\frac{12}{5}" align="absmiddle" class="latex-formula">