求（x+2y-1)(x-2y+1)-(x+2y+1)(x-2y-1)等于?

已知x+y=a,2x-y=-2a,求[（x/y-y/x)/(x+y)-x(1/x-1/y)]/[(x+1)/y]的值 若2/x-1/y=3,求[y/x-y/x-y(x-y/x-x+y)]/x-2y/x的值 x+2y=2x+y+1=7x-y 求：2x-y? 求(1+y)-2x(1+y)+x(1-y) (x-y)/(x+y)=3求( 3x-2y-1)/(x+y-5) 若x*x+y*y=x+y-1/2,求x,y的值如题 {(x+y)/2+(x-y)/3=1,(x+y)-5(x-y)=2.求x=?,y=? x+y=1,xy=-1/2,求x(x+y)(x-y)-x(x+y)2 已知:【(x²+y²)-(x-y)²+2y(x-y)】/4y=1,求4x/4x²-y²-1/2x+y 已知x-y=1,求[(x+2y)^2+(2x+y)(x-4y)-3(x+y)(x-y)]除以y的值大神们帮帮忙 已知x-y=1,求[(x+2y)²+(2x+y)(x-4y)-3(x+y)(x-y)]÷y的值 已知：2x+y=6,x-3y=1 求7y(x-3y)(x-3y)-2(3y-x)(3y-x) [(-x-y)(-x+y)-(x+y)^2-x(y-y^2)}÷1/2y x^2+y^2+x-y+1求最小值同上 y=arcsin(x/√1+x^2),求y' y=(1+x^2)的x次方,求y ' 求y‘-(1/x)y=x^2 的通解 y=ln(x+√x^2+1),求y