4x-7y=3-6 3x-2y=2急啊

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~ 1/(x+y)-1/(x-y)=-3/20,2/(x+y)+3/(y-x)=-(1/5)急啊! 几道 数学题急啊 对了再加20分(x+y)^2-(x+y)^3(x-y)^2-(x-y)^3 (x-y)^2-(y-x)^32(x-y)-3(y-x)^24ab(a+b)^2-6a^2b(a+b)(x+y)(x-y)-(x+y)^28a(x-y)^2-4b(y-x)a=-5 a+b+c=-5.2求代数式a^2(-b-c)-3.2a(c+b)的值 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 （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 {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 (x-y) (x-2y)+(x+2y) (x-3y)-2(x-3y) (x-4y)= x:y=3:4 y:z=2:1 x+y+z=20 急! 用代入法解下列方程组：（1）y=3x 16x-y=18 （2）3x+y=8 3x-y=4 (3)x+5y=5 2x-5y=10 (4)2x+y=3 x+2y=-6(5)x=2分之3y+7 y=3分之2x+8 (6)x-2=2(y-1) 2(x-2)+(y-1)要过程,十分急, 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= 若X-3Y=2,则7-2Y+6Y=多少?急 如果3x+2y=2,那么6x+4y-2=( )急急急！！！ 先化简,再求值：x-3(x+2y)+4(2y-x),其中x=-3,y=2 急