cosx cos(2x) -sinxsin(2x) = 0
cos(2x) = soc^2(x) - sin^2(x) and sin(2x) = 2sinxcosx
cosx(cos^2(x) - sin^2(x) ) - 2sinxsinxcosx = 0
cosx(cos^2x - sin^2x - 2sin^2x)= 0
cosx(cos^2x -3sin^2x) = 0
cos^2x = 1 - sin^2x
cosx(1-sin^2x -3sin^2x) = 0
cosx( 1 - 4sin^2x) = 0
cosx = 0 and 1-4sin^2x = 0
cos(p/2) = 0 and sin^2x =1/4
x = p/2 and sinx = 1/2
x=p/2 and sin(p/6) = 1/2
x = p/2 and x = p/6
p/2 = 90 degree and p/6 = 30 degree