｛x-2y=9 ｛3x-2y=-1 （用加减消元法）

x-y/x-x+y/y-(x+y)(x-y)/y² y/x=2 若2/x-1/y=3,求[y/x-y/x-y(x-y/x-x+y)]/x-2y/x的值 9y=3x-(x-1),4(x+y)-(2x+4)=8y x+y=1 5x-2y=8 3x-y=7 2x-y=3x表示y和用y表示x 3(x+y)-2(x-y)=11 4(x+y)+3(x-y)=9 (3x-y)^2+(3x+y)(3x-y),x=1,y=-2 4(x-y)-3(x-y)=9 5(x-y)+2(x-y)=11 二元一次方程 ：2(x+y)-(x-y)=3 (x+y)-2(x-y)=1 2(x+y)-3(x-y)=1 6(x+y)+(x-y)=51 {3(x+y)-4(x-y)=4 {x+y/2 + x-y/6=1 变量x,y满足约束条件,x+y>=3,x-y>=-1,2x-y (x-y)^2+(x+y)(x-y) 其中 X =3 Y=-1 (x-y)/(x+y)=3求( 3x-2y-1)/(x+y-5) 先化简再求值 x(9x-y)-y(y-x)+(x-y)的平方,其中x=-1,y=2 {(x+y)/2+(x-y)/3=1,(x+y)-5(x-y)=2.求x=?,y=? x+y+2(-x-y+1)=3(1-y-x)-4-(y+x-1),x+y=? (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