✔ 最佳答案
sinx+sin2x+sin3x+sin4x+sin5x=0
(sinx+sin5x)+(sin2x+sin4x)+sin3x=0
x+5x x-5x 2x+4x 2x-4x
2sin---cos---+2sin----cos----+sin3x = 0
2 2 2 2
6x -4x 6x -2x
2sin---cos---+2sin---cos---+sin3x = 0
2 2 2 2
2sin3xcos2x+2sin3xcosx+sin3x = 0
sin3x(2cos2x+2cosx+1) = 0
sin3x[2(2cos平方x-1)+2cosx+1] = 0
sin3x(4cos平方x-2+2cosx+1) = 0
sin3x(4cos平方x+2cosx-1) = 0
sin3x = 0 or 4cos平方x+2cosx-1 = 0
3x = 180n° x=360m°±72 or x=360k°±144
x = 60n°
where n, m, k are integer