Question

_ _ _ _ _ _ N ○ 309​

Answer 1

$cos150^\circ =cos(180^\circ -30^\circ )=-cos30^\circ =-\frac{\sqrt3}{2}\\\\\\sin135^\circ =sin(180^\circ -45^\circ )=sin45^\circ =\frac{\sqrt2}{2}\\\\\\cos120^\circ =cos(180^\circ -60^\circ )=-cos60^\circ =-\frac{1}{2}\\\\\\sin315^\circ =sin(360^\circ -45^\circ )=-sin45^\circ =-\frac{\sqrt2}{2}$

Answer 2

1) cos 150° = -cos 30° = $-\frac{\sqrt{3} }{2}$

2) sin 135° = sin 45° = $\frac{\sqrt{2} }{2}$

3) cos 120° = -cos 60° = $- \frac{1}{2}$

4) sin 315° = -sin 45° = $-\frac{\sqrt{2} }{2}$