原式=(5/2)(2sinxcosx- 2根号3*cos²x)
=(5/2)[sin2x- 根号3*(cos2x-1)]
=(5/2)(sin2x- 根号3*cos2x+根号3)
=5[(1/2)*sin2x- (根号3)/2 *cos2x] +5(根号3)/2
=5sin(2x- π/3) + 5(根号3)/2