请问老师{2x+3y=5 {2x-7y=-15怎么解方程组这是个方程组

请问老师{2x+3y=5 {2x-7y=-15怎么解方程组这是个方程组 已知x-y/x+y=3,求代数式5(x-y)/x+y-x+y/2(x-y) y 分之 x+2y =3分之7 请问x分之y 等于什么 x-y/x-x+y/y-(x+y)(x-y)/y² y/x=2 数学题不知为什么被老师全打错,求正确答案,x+y=3 x-y=2 x-y=-5 3x+2y=10 x+y=7 3x+y=17 x=3y 2x-y=5 4x-3y=17 y=7-5x 3x+y=10 4x-2y=73x+5y=5 3x-4y=23 x=2 y=1是方程mx-y=1 x-ny=7的解,求m,n的值两辆货车共运货20t,其中一辆比 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 解方程组(x+y)(x-2y)=-5 (x-y)(x+2y)=7 x+y/2+x-y/6=5 2(x+y)-3(x-y)=-2 {6(x-y)-7(x+y)=21 {2(x-y)-5(x+y)=-1 3(x+y)+2(x-y)=36 4(x+y)-5(x-y)=2 4(x-y)-3(x-y)=9 5(x-y)+2(x-y)=11 3(x+y)-4(x-y)=11,2(x-y)+5(x+y)=27 6(x-y)-2(x+y)=14 3(x-y)+(x+y)=5 若(x-y)/(x+y)=3 则(x+2y)/(6x-7y)等于 (x-y)/(x+y)=3求( 3x-2y-1)/(x+y-5) 请问 0=-5x+y-1 与 1=4x-3y+2 x*y的值是多少 先化简再求值(x-y)(x-2y)+(x-2y)(x-3y)-2(x-3y)(x-4y) x=4 y=5