x-y=3,x+y=1999,x、y的值

已知x-y=3,求[（x+y)(x-y)-(x-y)^2+2y(x-y)]除以的值 若2/x-1/y=3,求[y/x-y/x-y(x-y/x-x+y)]/x-2y/x的值 y=3(x-y),x=2(x-y)求x,y的值 已知|3x-y|+|x+y|=0,求x-y除以x*y的值. 根据x+x+x+y+y=54,x+x+y+y+y=56,求出x.y的值 x/3=y/4,求(x*x-xy)/(x*x+y*y)的值 已知XY.Y=-3,求-XY(X.X.X.Y.Y.Y.Y.Y.Y.Y-3.X.X.Y.Y.Y.Y.Y-Y)的值.（过程完整） 已知x-y=1,求[(x+2y)²+(2x+y)(x-4y)-3(x+y)(x-y)]÷y的值 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 x-y=3,x+y=1999,x、y的值 已知x-y=3,x+y=1999,求x,y的值 x+x+x+y+y=54 x+x+y+y+y=56 求y的值 已知(x+2y)(2x-3y)=y(y-4x),试求x/y的值 (x+y)(x+2y)(x+3y)(x+4y)=-40y的值为根号11 已知x,y为正整数,并且x*y+x+y=71,x*x*y+x*y*y=880,求3*x*x+8*x*y+3*y*y的值 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 (-x+6):(x-y);(4x+y)=3;14:1,求x+y的值. x-y/x-x+y/y-(x+y)(x-y)/y² y/x=2