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Re: integration

  • To: mathgroup at smc.vnet.net
  • Subject: [mg95999] Re: [mg95952] integration
  • From: DrMajorBob <btreat1 at austin.rr.com>
  • Date: Sat, 31 Jan 2009 06:45:32 -0500 (EST)
  • References: <200901301047.FAA06620@smc.vnet.net>
  • Reply-to: drmajorbob at longhorns.com

For instance...

Integrate[1/Sqrt[x^2 - b^2], x]

Log[2 (x + Sqrt[-b^2 + x^2])]

but

Log[2 (x + Sqrt[-b^2 + x^2])] - Log[x + Sqrt[-b^2 + x^2]] // Simplify

Log[2]

That's probably the kind of difference you're seeing between the online  
answer and the one you expect. -Log[b] is just a constant, after all.

Bobby

On Fri, 30 Jan 2009 04:47:06 -0600, <t.p.nixon 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?
>



-- 
DrMajorBob at longhorns.com


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