Question

2cosx+sqrt3=0 sin(2p-x)-cos(3p/2+x)+1=0 sin9p/4 cos(-4p/3)

Answer 1

$2cosx+\sqrt3=0\\cosx=-\frac{\sqrt3}{2}\\x=\pm arccos(-\frac{\sqrt3}{2})+2\pi n\\x=\pm\frac{\pi}{6}+2\pi n, \; n\in Z;\\\\sin(2\pi-x)-cos(\frac{3\pi}{2}+x)+1=0\\-sinx-sinx+1=0\\-2sinx=-1\\sinx=\frac{1}{2}\\x=(-1)^narcsin\frac{1}{2}+\pi n\\x=(-1)^n\frac{\pi}{6}+\pi n, \; n\in Z;\\\\sin\frac{9\pi}{4}=sin(\frac{8\pi}{4}+\frac{\pi}{4})=sin(2\pi+\frac{\pi}{4})=sin\frac{\pi}{4}=\frac{\sqrt2}{2};\\\\cos(-\frac{4\pi}{3})=cos(-(\frac{3\pi}{3}+\frac{\pi}{3}))=cos(\pi+\frac{\pi}{3})=-cos\frac{\pi}{3}=-\frac{1}{2}.$