Question

Cos α=3/5 3π/2< α< 2π. найти sinαs α=3/5 3π/2< α< 2π. найти sinα

Answer 1

$cosa=\frac{3}{5}\\\\\frac{3\pi}{2}<a<2\pi \; \; \; \to \; \; \; sina<0\\\\sina=-\sqrt{1-cos^2a}=-\sqrt{1-\frac{9}{25}}=-\sqrt{\frac{16}{25}}=-\frac{4}{5}$