4.2. cos α = −0,6, π/2 < α < π.

\(\cos\alpha=-0.6=-\frac{3}{5}\). Во II четверти синус положителен:

\(\sin\alpha=\sqrt{1-\frac{9}{25}}=\frac{4}{5}\).

\( g\alpha=-\frac{4}{3}\), \(\ctg\alpha=-\frac{3}{4}\).

Ответ: sin α = 4/5; tg α = −4/3; ctg α = −3/4.