4x-7y=3-6 3x-2y=2急啊

用加减法解下列方程组:3(x+y)-4(x-y)=-18 , 2分之(x+y)+6分之(x-y)=2求解啊,急~ x+y/2+x-y/3=6,4(x+y)-3(x-y)=-20 {(x+y)/2+(x-y)/3=6 4(x+y)-3(x-y)=-20 4(x+y)-3(x-y)=-20,2/x+y+3/x-y=6 {3(x+y)-4(x-y)=4 {x+y/2 + x-y/6=1 若(x-y)/(x+y)=3 则(x+2y)/(6x-7y)等于 4x-(2x+y+16)/2=-6y 2x+3y=7-x-2y 先化简,再求值：x-3(x+2y)+4(2y-x),其中x=-3,y=2 急 【2(x-y)^3-8(x-y)^2(x+y)+6y(x-y)^2】/2(x-y)^2= 化简,亲快啊啊急!(3x-2y)(7x-y)-（4x+3y）（x-y） 若2x-3y+4=0则x（x*x-1)+x(5-x*x)-6y+7 已知x/3=y/5=z/4,求x+y+z/y和x+y-z/y-x的值,2种方法.急等.