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Re: Why does this happen?

  • To: mathgroup at smc.vnet.net
  • Subject: [mg78724] Re: Why does this happen?
  • From: dh <dh at metrohm.ch>
  • Date: Sat, 7 Jul 2007 06:15:12 -0400 (EDT)
  • References: <f6ks38$lbm$1@smc.vnet.net>


Hi Budaoy,

look at your integrand. For large x you can neglect 1 and get 

Log[Exp[x]/Sqrt[x], but this is Log[Exp[x]]-Log[Sqrt[x]], where the 

first part is mach larger than the second. Therefore the integrand is 

approx.: x. This means, the integral does not exisit.

hope this helps, Daniel



Budaoy wrote:

> I have a problem in calculating this integral shown below:

> 

> Integrate[Log[1+Exp[x]/Sqrt[x]],{x,0,Infinity}]

> Pi^2/6

> 

> N[%]

> 1.64493

> 

> NIntegrate[Log[1+Exp[x]/Sqrt[x]],{x,0,Infinity}]

> 1.01799

> 

> Where does this difference come from and which one is correct?

> 

> 




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