已知x2-xy=5,xy-y2=-3,求代数式x2-y2和x2-2xy+y2的值.这样.那个x2是x的平方的意思,2xy是2乘xy的意思,因为键盘有限,打不出来,谢谢.

已知x2-3xy=-5,xy+y2=3,求x2-2xy+y2. 已知x2+y2 =7,xy=-2.求5x2 -3xy-4y2 -11xy-7x2 +2y2 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x/y=3/5,求 (x2-xy+2y2)/(x2+2xy-y2)的值 已知:x2+y2=7,xy=-2.求7x2-3xy-2y2-11xy-5x2+4y2已知:x2+y2=7,xy=-2.求7x2-3xy-2y2-11xy-5x2+4y2 已知x2+xy=3,xy+y2=-2,则2x2-xy-3y2= 已知2x2+5xy-3y2=0且xy不等于0,求x:y的值已知2x2+5xy-3y2=0且xy不等于0,求xy的值 已知x2+y2+4x-2y+5=0,求x2+2xy+y2值 已知x2+y2,x-y=5,求x2+y2和xy的值. 已知X/Y=2/7, 求X2-3XY+2Y2/2X2-3XY+7Y2的值 已知x/y=2/7,求分式(x2-3xy+2y2)/(x2-2xy+y2)的值 已知x/y=2/7,求分式x2-3xy+2y2/x2-2xy+y2的值 已知x+y=5,xy=-12,求代数式x2-xy+y2 已知x+y=4,xy=2,求x2+y2+3xy的值. 若3x2-4xy+y2=-3,2x2+3xy-2y2=8,求5x2-18xy+7y2的值. 已知X2次方+XY=3,XY+Y2次方=-2,求下例值:X2次方-Y2次方 已知实数x,y满足x2+xy+y2=3,则x2-xy+y2的最小值