x^2+y^2=5,(1)xy=2,(2)(1)+2*(2),(x-+y)^2=9x+y=3,-3(1)-2*(2)(x-y)^2=1x-y=1,-1联立得,x+y=3,x-y=1,x=2.y=1x+y=3,x-y=-1,x=1,y=2x+y=-3,x-y=1,x=-1,y=-2x+y=-3,x-y=-1,x=-2,y=-1