(2) sin2x=u2,u=sinx d(sin2x)d(u2)d(sinx) dx du dx =2u.cosx=2sin xcosx=sin2x(2) sin x u , u sin x 2 2 = = dx d x du d u dx d(sin x) ( ) (sin ) 2 2 =  = 2u cos x = 2sin xcos x = sin 2x