solve sin5x-sin3x+sinx = 0, --> means finding values of x for 0deg (< or =) x (< or =) 180deg Solution inP - sinQ = 2cos½(P+Q)sin½(P-Q) therefore sin5x-sin3x=2cos4xsinx sin5x - sin3x +sinx = 2cos4xsinx + sinx = 0 sinx(2cos4x+1) = 0 sinx = 0 x=0,180 OR 2cos4x+1=0 cos4x = - ½ if 0.