2x^2-4x+4/x-1
=[2(x-1)^2+2]/(x-1)
=2[(x-1)+1/(x-1)]>=2*2√(x-1)*1/(x-1)=4
最小值=4若x∈R+,则x/x^2+1有最 值,且此最值是帮帮忙，会提高悬赏。x/x^2+1=1/(x+1/x)x+1/x>=2所以x/x^2+1=1/(x+1/x)<=1/2最大值为1/2.