Упростить: а)sin(90-13)= б)sin(-90-31)= в)cos(-90+17)= Выразить число через синус или...

$sin(90^o-13^o)=cos 13^o;$

$sin(-90^o-31^o)=-sin(90^o+31^o)=-cos 31^o;$

$cos(-90^o+17^o)=cos(90^o-17^o)=sin 17^0;$

$cos \frac{\pi}{3}=cos (\frac{\pi}{2}-\frac{\pi}{6})=sin \frac{\pi}{6};$

$sin \frac{5*\pi}{7}=sin(\pi-\frac{2*\pi}{7})=sin(\frac{2*\pi}{7})=sin (\frac{\pi}{2}-\frac{3*\pi}{14})=cos \frac{3*\pi}{14};$

$cos \frac{14*\pi}{5}=cos (2*\pi+\frac{4*\pi}{5})=cos \frac{4*\pi}{5}=cos (\pi-\frac{\pi}{5})=-cos \frac{\pi}{5}$