[TEX]sinx+sin2x+sin3x+sin4x+sin5x+sin6x=0 \\ sinx+sin6x+sin3x+sin4x+sin5x+sin2x=0 \\ sin(\frac{7x}{2}).cos(\frac{5x}{2}) + sin(\frac{7x}{2}).cos(\frac{x}{2}) +sin(\frac{7x}{2}).cos(\frac{3x}{2}) = 0 \\ sin(\frac{7x}{2}) = 0 \\ cos(\frac{5x}{2}) + cos(\frac{x}{2}) + cos(\frac{3x}{2}) = 0 \\ 2cos(\frac{3x}{2}).cosx + cos(\frac{3x}{2}) = 0 \\ cos(\frac{3x}{2} )= 0 \\ cosx = - \frac{1}{2}[/TEX]