(等比级数)求(x-y)+[(y^2/x)-(y^3/x^2)+(y^4/x^3)-(y^5/x^4)+.n项的和

(等比级数)求(x-y)+[(y^2/x)-(y^3/x^2)+(y^4/x^3)-(y^5/x^4)+.n项的和 已知x-y/x+y=3,求代数式5(x-y)/x+y-x+y/2(x-y) 已知|2-x|与|x-y+4|互为相反数,求代数式3(x-y)-5(x-y)-3(x-y)+(y-x)-4(x+y)+3 已知x=1/3,y=-1/2,求代数式x-(x+y)+(x+2y)-(x+3y)+(x+4y)-(x+5y)+...-( 求5x-2y=x-y=4x-3y-2的解 1.已知:x-2y=3,求[(3x+2y)(3x-2y)-(x+2y)(5x-2y)]除4x 的值 已知x-2y=2011,求[(3x+2y)(3x-2y)-(x+2y)(5x-2y)]÷4x的值. 已知2x-y/x+3y=2,求代数式4x-2y/x+3y减4x+12y/2x-y的值 （x+2)(x+3) (x-4)(x+1) (y+4)(y-2) (y-5)(y-3) 已知x/3=y/5=z/4,求x+y+z/y和x+y-z/y-x的值,2种方法.急等. 3(x+y)-4(x-y)=11,2(x-y)+5(x+y)=27 (x+3y-4)(2x-y)