已知X2+XY=2,Y2+XY+5,求1/2X2+XY+1/2Y2的值?

已知x2-xy=3，xy-y2=-5，试求代数式x2+2xy-3y2的值． 已知x2+y2=7,xy=-2,求5x2—3xy—4y2—11xy—7x2+2y2的值 已知X2+y2=7,Xy=-2,求多项式5X2一3Xy-4y2-11Xy-7X2+2y2的值. 已知：x2+y2=7，xy=-2．求7x2-3xy-2y2-11xy-5x2+4y2的值． 已知2x=3y,求xy／(x2+y2)-y2／(x2-y2)的值 已知x2-xy=-3，2xy-y2=-8，求2x2+4xy-3y2的值． 已知x2+xy=-3，xy+y2=7，试求：x2+2xy+y2的值． 已知x2+4y2+x2y2-6xy+1=0,求 x4-y4/2x-y 乘 2xy-y2/xy-y2 除以（x2+y2/x 已知x2-xy=21，xy-y2=-12，分别求式子x2-y2与x2-2xy+y2的值． 已知x2+xy=4,xy+y2=12,求代数式x2-y2与x2+2xy+y2的值各为多少 已知x(x-1)-(x2-y)=-3,求x2+y2-2xy的值 已知x-y+1,X2+Y2=25 求（x+y）2和x2-xy+y2的值