解：设x/2=y/3=z/4=t则：x=2t y=3t z=4t (2x+3y-z)/(x-3y+z)=(4t+9t-4t)/(2t-9t+4t)=-9t/3t=-3
令x/2=Y/3=Z/4=k所以x=2k;y=3k;z=4k;代入化简出来答案了吧
