{(x+y)²-(x-y)²}÷(-4xy)= (3xy-y)÷y=

[-(x-y)^2/xy]^-4*(y^2-xy/x)^3*(x^4/y^10)÷(xy-y^2/x)^-5=-y(y- 已知2x+y=0,求x-2y/x²+xy乘(x²-y²)÷x²-4xy+4y&# 已知xy=-2,x-y=3,求（x+y)（x-y)-y^2+（x-y)^2-（6x^2y-2xy^2)÷2y x-y/x²÷x²-2xy+y²/xy*（xy-x²） 已知x²+y²-8x+6y+25=0,求（x-y+4xy/x-y）（x+y-4xy/x+y） 急![(3x+y)²-3(3x-y)(x+y)-(x-3y)(x+3y)]÷(2xy) 已知x/y=2,求2x(x+y)-y(x+y)/4x²-4xy+y² 已知x,y满足x²+y²-4x-6y+13=0,求（- y/x^3)^3÷(- 1/xy)^4.(x 已知|3-y|＋|x+y|=0,求[2(x+y)-3(xy+4)]÷1／xy的值. x²+xy/(x-4y)(x+y),其中x=4,y=-1 X²+2xy+y²/xy乘x²-2xy+y²/xy+y²= 4x²y³÷(-½xy)²=