Question

Дано cos α=0.6
П<α 3П\2

Найти: sinα,tg(П/2+α)

Answer 1

$cosa=-0,6\\\\sin^2a=1-cos^2a\; \; \to \; \; \; sina=\pm \sqrt{1-cos^2a}\\\\\pi <a<\frac{3\pi }{2}\; \; \to \; \; cosa<0\; ,sina<0\; \; ,\; \; sina=-\sqrt{1-(-0,6)^2}=-0,8\\\\tg(\frac{\pi}{2}+a)=-ctga=-\frac{cosa}{sina}=-\frac{-0,6}{-0,8}=\frac{6}{8}=-0,75$