(-1/2xy^2)-1/6x(xy^3)^2=?

[6xy-3(xy-1/2x的平方y]/3xy=? 3xy乘以[6 xy-3(xy-1/2x的平方y)] 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 ①(9x²y-6xy²)÷3xy ②(3x²y-xy²+2分之1xy)÷(-2分之1xy) 1-(3xy-x)+【-2(2x+3xy)】 计算3xy[2xy-x(y-2)+x-1] 已知（x+1）*（x+1）=-Iy-1I,求2（xy-（5xy）*（5xy））-3（（xy）*（xy）-xy） (-xy^-1)^2*(-xy^-2)^-3/(-x^2y^3) y^3+xy^2+2xy+x^2-1 因式分解 5x^2y/-1/2xy*3xy^2 ( )-(x^2+3xy)=-xy-1/3y^2 xy(xy+1)+xy+3-2(x+y+1/2)-(x+y-1)^2因式分解 (-1/3xy)^2•[xy(2x-y)-2x(xy-y^2)] (-3分之1xy)的平方×[xy(2x-y)-2x(xy-y的平方)] 1-2/x+y=xy,4y+6x=xy.求xy的解? XY(XY+3)+(XY+4)+4(X+Y+1)-(X+Y+2) 当x=3,y=3分之1时,求代数出3xy-[2xy-2(xy-2分之3xy)+xy]+3xy的值 5xy^2-{2x^y-[3xy^2-（xy^2-2x^2y）]/（-1/2xy）}