|x+2|+|x-1|=9-|y+1|-|y-5|求x+y的最大值与最小值.

先化简再求值 x(9x-y)-y(y-x)+(x-y)的平方,其中x=-1,y=2 9y=3x-(x-1),4(x+y)-(2x+4)=8y 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-y)(x+y)-(x+y)^2+2y(y-x),其中x=1,y=3. 2y(x+二分之一y)-[(x+y)(x-y)+2y(y+x)],其中|x-1|=2 1-x+y-2x+9y= (x-y)/4+(x+y)/5=1/4 (x+y)/9-(x-y)/3=//2(x-y)/4+(x+y)/5=1/4(x+y)/9-(x-y)/3=//2 解方程组 3(x+y)-2(x-y)=9,5(x+y)+2(x-y)=-1 解方程组:{3(x+y)-2(x-y)=9,5(x+y)+2(x-y)=-1} 解二元一次方程 {3(x+y)-4(x-y)=-9 x+y/2+x-y/6=1 已知4x=9y求(1)x+y/y (2)y-x/2x有关比例的 设x,y满足约束条件x+y>=1,x-y>=-1,2x-y 设x,y满足约束条件x+y>=1,x-y>=-1,2x-y x+2y=2x+y+1=7x-y 求：2x-y? y=(2x)/x-1化简成用y表示x 二元一次方程 ：2(x+y)-(x-y)=3 (x+y)-2(x-y)=1 (3x-y)^2+(3x+y)(3x-y),x=1,y=-2