（21x^4y^3-35x^3y^2+7x^2y^2）÷【】=-3x^2y^2+5xy-y.【】里填什么?

（21x^4y^3-35x^3y^2+7x^2y^2）÷【】=-3x^2y^2+5xy-y.【】里填什么? 计算(x^8-x^7y+x^5y^3-x^4y^4+x^3y^5-x^y^7+y^8)(x^2+xy+y^2) x^8-x^7y+x^6y^2-x^5y^3+x^4y^4-x^3y^5+x^2y^-xy^7+y^8 [-(x-y)^2/xy]^-4*(y^2-xy/x)^3*(x^4/y^10)÷(xy-y^2/x)^-5=-y(y- 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) 已知xy=-2,x-y=3,求（x+y)（x-y)-y^2+（x-y)^2-（6x^2y-2xy^2)÷2y (2x-y)(2x+y)+(2x-y)(y-4x)+2y(y-3x)+2x^4y^2÷(xy)^2 已知3x^2+xy-2y^2=0,求{(x+y)/(x-y)+4xy/(y^2-x^2)}/{(x+3y)*(x-y)} [x(x^2y^2-xy)-y(x^2-x^3y)]/3x^2y (x+y)(x-y)-(2xy+3y)平方 已知（x+2）^2+|x+y+5|=0,求3x^2y-[2x^2y-(2xy-x^2y)-4x^2]-xy