Question

Среди величин положительной является: 1)sin 2)cos 3)tg 4)cos 5)sin

Answer 1

$sin\frac{4\pi}{3}=sin(\pi +\frac{\pi}{3})=-sin\frac{\pi}{3}\ \textless \ 0\\\\cos\frac{14\pi}{15}=cos(\pi-\frac{\pi}{15})=-cos\frac{\pi}{15}\ \textless \ 0\\\\tg\frac{8\pi}{9}=tg(\pi-\frac{\pi}{9})=-tg\frac{\pi}{9}\ \textless \ 0\\\\cos\frac{9\pi}{8}=cos(\pi +\frac{\pi}{8})=-cos\frac{\pi}{8}\ \textless \ 0\\\\sin\frac{4\pi}{5}=sin(\pi-\frac{\pi}{5})=sin\frac{\pi}{5}\ \textgreater \ 0$