2-[-3(-3/1-3/2xy)-2y²]-2(x²-xy+2y²) x=2/1 y=-1是不是-3又2/1

2x²y-3(2xy-xy)-xy (-1/3xy)^2•[xy(2x-y)-2x(xy-y^2)] xy(xy+1)+xy+3-2(x+y+1/2)-(x+y-1)^2因式分解 (-3分之1xy)的平方×[xy(2x-y)-2x(xy-y的平方)] XY(XY+3)+(XY+4)+4(X+Y+1)-(X+Y+2) (-xy^-1)^2*(-xy^-2)^-3/(-x^2y^3) ( )-(x^2+3xy)=-xy-1/3y^2 y^3+xy^2+2xy+x^2-1 因式分解 5x^2y/-1/2xy*3xy^2 计算 -6xy(-1/3xy+2/3y-1) 计算3xy[2xy-x(y-2)+x-1] 5xy^2-{2x^y-[3xy^2-（xy^2-2x^2y）]/（-1/2xy）} (-3xy+2xy)-(4xy+xy) 化简!1、（x^2-xy）+xy+y^2 2、3（x^2-xy）-xy+y^2 若1/x-1/y=2,求3x-2xy-3y/x-xy-y的值3x-2xy-3y/x-xy-y 不好意思，是3x-2xy-3y/x-2xy-y x^2-xy-6y^2+3xy+y+2 2y+3xy因式分解 已知1/x-1/y=2,求3x+7xy-3y/2x-3xy-2y答案是1/x-1/y=2(y-x)/xy=2 得：x-y=-2xy(3x+7xy-3y)/(2x-3xy-2y)=[3(x-y)+7xy]/[2(x-y)-3xy]=(-6xy+7xy)/(-4xy-3xy)=xy/(-7xy)=-1/7 谁能帮我解释一下=[3(x-y)+7xy]/[2(x-y)-3xy]=(-6xy+7xy)/(-4xy-3xy) 是怎