｛2x-5y=21,{2x+y=6 {x-3y=1 {y=-2x+3 y=-x; y=1/2x+1 5x-9y=-13 y=3x-7

{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/2+x-y/6=5 2(x+y)-3(x-y)=-2 6(x-y)-2(x+y)=14 3(x-y)+(x+y)=5 已知x-y/x+y=3,求代数式5(x-y)/x+y-x+y/2(x-y) 解方程组6(x-y)-7(x+y)=21 2(x-y)-5(x+y)=-1 6（x-y)-7(xy)=21,2(x-y)-5(x+y)=-1 3x+5y-(x+y)=6 2(x+y)-3x=-7 【2(x-y)^3-8(x-y)^2(x+y)+6y(x-y)^2】/2(x-y)^2= X^2-Y^2+6X+10Y-30=0 X^2+Y^2-5X-8Y+21=0 X=?Y=? （x+y）/2- x-y/2=6 3(x+y)=4(x-y) x+y/3+x-y/2=6 4(x+y)-2(x-y)=40 [(2x-y)(2x+y)+y(y-6x)]÷2x=? 解方程组(x+y)(x-2y)=-5 (x-y)(x+2y)=7 3(x+y)+2(x-y)=36 4(x+y)-5(x-y)=2 x*x+2x+y*y-4y+5=0 x= y= 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