sinx+siny=根号2 (1)cosx+cosy=2根号3/3 (2)(1)平方+(2)平方2+2sinxsiny+2cosxcosy=2+4/3cosxcosy+sinxsiny=2/3 (3)cos (x-y)=2/3 (4)(2)平方-(1)平方cos2x+cos2y+2(cosxcosy-sinxsiny)=-2/32cos(x+y)cos(x-y)+2cos(...