y=x2+2x+1、x-1,x-1>0求最值

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y=x2+2x+1、x-1,x-1>0求最值
到底等于多少,有好几个答案
y=x2+2x+1/x-1，x-1>0

y=(x^2+2x+1)/(x-1)
=(x^2-2x+1+4x)/(x-1)
=x-1+4(x-1+1)/(x-1)
=x-1+4/(x-1)+4
≥2*2+4=8
仅当x-1=4/(x-1)时成立,又x-1>0,即x=3
综上所述,无最大值,当x=3时,取得最小值y=8

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