y=5/x ,y=x/2 ,y=2a/x ,y=5-x ,xy=2 ,a≠0 ,y=(-2)/5x ,y=(-2)/5-

若(x*x+y*y)(x*x+y*y)-4x*x*y*y=0,求代数式(x*x+5xy+y*y)/(x*x+2xy+y* 已知x-y/x+y=3,求代数式5(x-y)/x+y-x+y/2(x-y) 已知x,y>0 2x+y+3=xy 求5x+4y最小值 已知x+y=-1,xy=-2,求代数式-5（x+y)+(x-y)+x(xy+y)的值 [-(x-y)^2/xy]^-4*(y^2-xy/x)^3*(x^4/y^10)÷(xy-y^2/x)^-5=-y(y- 已知x²+y²-2x+4y+5=0,求X^4-y^4/2x^2+xy-y²·2x-y/xy 已知x*x-4xy+4y*y=0 求[2x(x+y)-y(x+y)]/(4x*x-4xy+y*y)的值? 先化简再求值(x-y)(x+y)-(x-2y) 的完全平方+x(3x-5y)-(x-y)(x-2y),其中x=1/2 y 已知x*x+4x+y*y-2y+5=0,则x*x+y*y=? x-y / 5y= (y-x)^2 / ( ) f(x+y,x-y)=2x②+5xy+2y②+6求f(x,y) 已知x+4y-2x+8y+5=0,求x^4-y^4/2x+xy-y·2x-y/xy-y÷(x+y/y)的值.