1.5x-2y=-1 -4.5x+7y=8

x+2y=2x+y+1=7x-y 求：2x-y? {6(x-y)-7(x+y)=21 {2(x-y)-5(x+y)=-1 x-y/x-x+y/y-(x+y)(x-y)/y² y/x=2 (x-y)(x-2y)+(x-2y)(x-7y),其中X=4,Y=1.5 已知：2x+y=6,x-3y=1 求7y(x-3y)(x-3y)-2(3y-x)(3y-x) [3x^2-(x+y)(y-x)][2(-x-y)(y-x)+2x^2+3y^2],其中x=-2分之1,y=1.5 x+y=1 5x-2y=8 3x-y=7 2x-y=3x表示y和用y表示x （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 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 1x=0.5y 2x=2y 3x=4.5y 求规律.（如y＝...）如果y是1.5,x是多少? 解方程组(x+y)(x-2y)=-5 (x-y)(x+2y)=7 x^2+y^2=15,x+y=7,x＞y,求x-y 当x+y=2时7(x+y)一(x+y)+(x+y)=? 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 二元一次方程 ：2(x+y)-(x-y)=3 (x+y)-2(x-y)=1