-(2x^20-7xy)-2[2x^2-(3x^2-5xy+y^2)]化简

（xy-x^2)乘以(xy)/(x-y) x^3y(-4y)^2+(-7xy)^2*(-xy)-5xy^3*(-3x)^2 (x-2xy)*(-xy+2y*y)-(3x*x-2xy)(x-9xy+6y*y) （x^2+xy/x-y)/（xy/x-y)计算 计算3xy[2xy-x(y-2)+x-1] 计算：3xy[2xy-x（y-2）+x] （-3x^y+2xy)-( )=4x^+xy 化简：x-y/x+3y÷x^-y^2/x^2+6xy+9y^2-(xy/x+y) 1、(-7x^y)(2x^y-3xy^3+xy) 2、((x-y)^6)/((y-x)^3)/(x-y) 5x^2y/-1/2xy*3xy^2 -3(xy-2x²)-[y²-(5xy-4x²)+2xy] 化简!1、（x^2-xy）+xy+y^2 2、3（x^2-xy）-xy+y^2