0\\\\\\cos^2a=1-sin^2a=1-(-0,6)^2=1-0,36=0,64\\\\\\cosa=-\sqrt{0,64}=-0,8" alt="19.2.\ \ \ sina=-0,6\\\\\\a\in \Big(\pi ;\dfrac{3\pi }{2}\Big)\ \ \ \to \ \ \ \ cosa0\ ,\ \ ctga>0\\\\\\cos^2a=1-sin^2a=1-(-0,6)^2=1-0,36=0,64\\\\\\cosa=-\sqrt{0,64}=-0,8" align="absmiddle" class="latex-formula">
