text: cosxsin2x=0? trigonometric equations cosxsin2x=0 cosx*2sinxcosx=0 2sinx(cosx)^2=0 sinx(cosx)^2=0   sinx=0                          x=0 or 180 degrees (x=o or x=π)      or cos^2x=0, so cosx=0 x=90 or 270 degrees (x=π/2 or 3π/2)