高一求函数最值题

f(x)=(x-1)/(x+ 1)=(x+1-2)/(x+1)=1-2/(x+1),
由于:2<=x+1<=4,故1/4<=1/(x+1)<=1/2
-1<=-2/(x+1)<=-1/2
0<=1-2/(x+1)<=1/2
所以,0<=f(x)<=1/2,即值域是[0,1/2]