X＞-1,x+1>0
f（x）=(x＾2-3x+1)/(x+1)=x-[4x-1/x+1]
=x-4+5/(x+1)=(x+1)+5/(x+1)-5>=2√[5(x+1)/(x+1)]-5
=2√5-5
f（x）=x＾2-3x+1/x+1的值域
f(x)>=2√5-5