1.已知x2-xy=5,xy-y2=-3.求式子3(x2-xy-xy+y2)的值
已知x2-xy=3,xy-y2=-5,试求代数式x2+2xy-3y2的值.
已知x2-xy=21,xy-y2=-12,分别求式子x2-y2与x2-2xy+y2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+xy=3,xy+y2=-2,则2x2-xy-3y2的值为( )
已知2x=3y,求xy/(x2+y2)-y2/(x2-y2)的值
已知x2;+xy=3,xy+y=-2,求代数式2x2;-xy-3y2;的值
已知X2-2x+y2+6y+10=0,求(x2-2xy)/(xy+y2)的值
已知x+y=4,xy=2,求x2+y2+3xy的值.