x/2=y/3=z/4≠0可推出y=3/2x,z=2x所以2x+3y-z=2x+9/2x-2x=9/2x x-2y+3z=x-3x+6x=4x(2x+3y-z)/(x-2y+3z)=9/8
设x/3=y/4=z/5=k 所以 x=3k y=4k z=5k 所以 (x+y-z)/(x-y+z) =（3k+4k-5k）/(3k-4k+5k) =2k/4k =1/2 祝学习进步
