Question

1)cos^2x=1/2+sin^2x 2)4sinxcosx cos 2x=1 3)sinx*cos(x+pi/3)+cosx*sin(x+pi/3)=0

Answer 1

1/   $cos^2x-sin^2x=\frac{1}{2}\\ cos2x=\frac{1}{2}\\ 2x=+-\frac{\pi}{3}+2\pi*k\\ x=+-\frac{\pi}{6}+\pi*k$

2/   $sin2x=2sinx*cosx\\ sin4x=2sin2x*cos2x=4sinx*cosx*cos2x\\ 4sinx*cosx*cos2x=1\\ sin4x=1\\ 4x=\frac{\pi}{2}+2\pi*n\\ x=\frac{\pi}{8}+\frac{\pi*n}{2}$

3/   $sin(a+b)=sina*cosb+cosa*sinb\\ sinx*cos(x+\frac{\pi}{3})+cosx*sin(x+\frac{\pi}{3})=0\\ sin(x+x+\frac{\pi}{3})=0\\ 2x+\frac{\pi}{3}=\pi*k\\ x=\frac{\pi*k}{2}-\frac{\pi}{6}$