4.6. cos α = 12/13, 3π/2 < α < 2π.

В IV четверти sin α < 0.

\(\sin\alpha=-\sqrt{1-\frac{144}{169}}=-\frac{5}{13}\).

\( g\alpha=-\frac{5}{12}\), \(\ctg\alpha=-\frac{12}{5}\).

Ответ: sin α = −5/13; tg α = −5/12; ctg α = −12/5.