求（x+2y-1)(x-2y+1)-(x+2y+1)(x-2y-1)等于?

1、x(x-y)(x+y)-x(x+y)^2 (1)(x^2/x)-y-x-y 当x-y/x+y等于1/2时,求y-x／x+y减去2x+2y／x-y [(-x-y)(-x+y)-(x+y)^2-x(y-y^2)}÷1/2y 1/2X-1/X+Y*(X+Y/2X-X-Y)等于多少, 设x>1,y>0,若x^y+x^-y=2根号2,则x^y-x^-y等于 已知4x=9y求(1)x+y/y (2)y-x/2x 求（x+2y-1)(x-2y+1)-(x+2y+1)(x-2y-1)等于? (1)(x+y)^2-(x-y)^2 1、(x-2y)(x+y) x+y=1,xy=-1/2,求x(x+y)(x-y)-x(x+y)2 已知x=1/3,y=-1/2,求代数式x-(x+y)+(x+2y)-(x+3y)+(x+4y)-(x+5y)+...-(