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(因为不等于0,所以可以把x约分掉)
令a=x/2=y/3=z/4则x=2a,y=3a,z=4a所以原式=(4a+9a-4a)/(2a-9a+12a)=9a/5a=9/5
令x/2=y/3=z/4=k,则x=2k,y=3k,z=4k,那么(2x+3y-z)/(x-2y+3z)=9/8