xy+xy=20,x=,y=

xy+x=20 xy+y=18 xy'=y+xy的 x-xy=40,xy-y= -20,求代数式x-y和x+y-2xy 已知:x-xy=40,xy-y=-20,求代数式x-y和x+y-2xy的值. x^2+xy+x=36,y^2+xy+y=20,求x+y. [(xy-2)(-xy-2)-4(xy-1)^2]除以(-xy),其中x=20,y=-25分之1 （-3x^y+2xy)-( )=4x^+xy X²+2xy+y²/xy乘x²-2xy+y²/xy+y²= .先化简,后计算.[2x(x²y-xy²)+xy(xy-x²)]/x²yx=20 先化简,再求值 ⒈2(Xy+Xy)-3(Xy-xy)-4Xy,其中X=1,y=-1 已知x-xy=8,xy-y=-9,求x+y-2xy的值 已知x-y=4xy，则2x+3xy-2yx-2xy-y