Question

Определите знак cos 305° и tg(-6п/5)

Answer 1

$cos\, 305=cos(360-55)=cos(-55)=cos55\ \textgreater \ 0,\; \\\\tak\; kak\; \; \; 0^\circ \ \textless \ 55^\circ \ \textless \ 90^\circ \\\\\\tg(- \frac{6\pi }{5})=-tg\frac{6\pi}{5}=-tg(\pi +\frac{\pi}{5})=-tg\frac{\pi}{5}\ \textless \ 0;\\\\tak\; kak\; \; \; 0\ \textless \ \frac{\pi}{5}\ \textless \ \frac{\pi }{2} \; \; \Rightarrow \; \; tg \frac{\pi}{5} \ \textgreater \ 0\; \; \Rightarrow \; \; -tg \frac{\pi}{5}\ \textless \ 0\; .$