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Re: integration

  • To: mathgroup at smc.vnet.net
  • Subject: [mg95967] Re: integration
  • From: dimitris <dimmechan at yahoo.com>
  • Date: Sat, 31 Jan 2009 01:12:37 -0500 (EST)
  • References: <glvkh7$e73$1@smc.vnet.net>

On 30 =C9=E1=ED, 21:30, t.p.ni... at open.ac.uk wrote:
> Hi, I don't use mathematica but the other day I wanted to solve an
> integral and I'm out of practice so I went on-line to a mathematica
> based integrator.
>
> http://integrals.wolfram.com/index.jsp
>
> I typed in 1/sqrt(x^2-b^2) this should have an integral of cosh^-1(x/
> b).  Ok, so it didn't recognize cosh but its answer was (I think)
> wrong.  it comes back with ln(x+sqrt(x^2-b^2)) it seems to have
> overlooked a quotient of b in the log.
>
> Is this a general problem with mathematica or just the on-line version
> or is it me?

Everything is ok!

In[683]:= Integrate[1/Sqrt[x^2 - b^2], x]
D[%, x] // Together(*check*)

Out[683]= Log[x + Sqrt[-b^2 + x^2]]

Out[684]= 1/Sqrt[-b^2 + x^2]

Dimitris



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