y=2sinxcosx+cos2x因为sin2x=2sinxcosx所以y=sin2x+cos2x再变为y=√2(√2/2sin2x+√2/2cos2x)因为sinπ/4=cosπ/4=√2/2所以y=√2(cosπ/4sin2x+sinπ/4cos2x)根据sin(α+β)=sinαcosβ+cosαsinβ可得y=√2sin(2x+...