0\\\\cos \alpha =+\sqrt{1-sin^2 \alpha }=\sqrt{1-\frac{16}{25}}=\sqrt{\frac{9}{25}}=\frac{3}{5}" alt="sin \alpha =-\frac{4}{5},\quad \alpha \in 1V\; chetverti\; \to cos \alpha >0\\\\cos \alpha =+\sqrt{1-sin^2 \alpha }=\sqrt{1-\frac{16}{25}}=\sqrt{\frac{9}{25}}=\frac{3}{5}" align="absmiddle" class="latex-formula">