tg(-870°) = - tg(870°) = - tg(720° + 150°) = - tg(150°) = - tg(180° - 30°) (2 четверть) = - (- tg(30°)) = tg(30°) = √3/3

соs(330°) = cos (360° - 30°) (4 четверть) = cos 30° = √3/2

[tex] \frac{1}{2} \times \frac{ \sqrt{3} }{3} \times \frac{ \sqrt{3} }{2} = \frac{3}{2 \times 3 \times 2} = \frac{1}{4} = 0.25[/tex]