令a=x/2=y/3=z/4x=2a y=3a z=4a(x+y+z)/(x+y-z)=(2a+3a+4a)/(2a+3a-4a)=9a/a=9
已知X/2=y/3=z/4≠0，求(x+y+z)/(x+y-z)的值解：设x/2=y/3=z/4=m，则x=2m，y=3m，z=4m，故(x+y+z)/(x+y-z)=(2m+3m+4m)/(2m+3m-4m)=9m/m=9
