5sinxcosx-5根号3cos^2x+2分之5根号3
=5/2 sin2x-5根号3*(cos2x+1)/2+5/2 根号3
=5/2 sin2x-5/2 根号3 cos2x
=5[1/2sin2x-根号3/2 cos2x]
=5sin(2x-60)