｛x+y=7 ｛2x-5y=-21

{6(x-y)-7(x+y)=21 {2(x-y)-5(x+y)=-1 解方程组(x+y)(x-2y)=-5 (x-y)(x+2y)=7 x-y/x-x+y/y-(x+y)(x-y)/y² y/x=2 ｛x+y=7 ｛2x-5y=-21 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 已知x-y/x+y=3,求代数式5(x-y)/x+y-x+y/2(x-y) 3x+5y-(x+y)=6 2(x+y)-3x=-7 x+y=1 5x-2y=8 3x-y=7 2x-y=3x表示y和用y表示x x+x+y+y+y=21 ,x+x+y+y+y+y+y=27 ,x ,y=? x+x+y+y+y=21 ,x+x+y+y+y+y+y=27 ,x ,y=? 4.4x+6y=54 9x+2y=87 5.2x+y=7 2x+5y=19 6.x+24.4x+6y=54 9x+2y=87 5.2x+y=7 2x+5y=19 6.x+2y=21 3x+5y=56 把(x-y)看作一个整体,化解:5(x-y)+2(x-y)-4(x-y)= 3(x-y)把(x-y)看作一个整体,化解:5(x-y)+2(x-y)-4(x-y)=3(x-y)²-4(x-y)+7(x-y)-6(x-y)²= 2(x-y)=5y,x-y=-5 x+2y=2x+y+1=7x-y 求：2x-y? 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)=? x-y / 5y= (y-x)^2 / ( )