设x/2=y/3=z/4=k
则x=2k y=3k z=4k
3x+2y-z分之x-y-z
=(x-y-z)/(3x+2y-z)
=(2k-3k-4k)/(3*2k+2*3k-4k)
=(-5k)/(8k)
=-5/8呵呵.我也在做这道题.