(x-1/2y)/(1/2x+y)=(2x-y)/(x+2y)变形正确吗

1、x(x-y)(x+y)-x(x+y)^2 (1)(x^2/x)-y-x-y [(-x-y)(-x+y)-(x+y)^2-x(y-y^2)}÷1/2y 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 判断下列变形是否正确?1/x-y=(x+y)²/(x-y)(x+y)² 请说明原因 (3x-y)^2+(3x+y)(3x-y),x=1,y=-2 已知4x=9y求(1)x+y/y (2)y-x/2x {3(x+y)-4(x-y)=4 {x+y/2 + x-y/6=1 (1)(x+y)^2-(x-y)^2 1、(x-2y)(x+y) y=(x^2+x)/(x+1) 2(x+y) 3x+3y=24 x+y/2x x y/2y= 1