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MathGroup Archive 2001

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Re: Simple indefinite integral disagrees with table

  • To: mathgroup at smc.vnet.net
  • Subject: [mg28660] Re: Simple indefinite integral disagrees with table
  • From: Ignacio Rodriguez <ignacio at sgirmn.pluri.ucm.es>
  • Date: Sat, 5 May 2001 04:00:44 -0400 (EDT)
  • Organization: UCM
  • References: <9ctb6k$m4h@smc.vnet.net>
  • Sender: owner-wri-mathgroup at wolfram.com

If you use brakets, Mathematica takes Cos to be a constant and just multiplies:

Integrate[x Cos (a x),x] -> 1/3 a Cos x^3

This is just

Integrate[a x^2 Cos,x]-> 1/3 a Cos x^3

If you want Cos to be the cosine function, just use

Integrate[x Cos[a x],x] -> (Cos[a x]+a x Sin[a x])/a^2

which is what you have in your table.

Mitch Berkson wrote:

> The Mathematica solution to the indefinite integral below doesn't agree with
> that found in my CRC tables.
>
> Integrate[xx Cos (aa xx), xx]
> = (1/3) aa Cos xx^3
>
> The CRC table gives: (1/aa^2) Cos (aa xx) + (xx/aa) Sin (aa xx)
>
> The Mathematica solution doesn't look right.  Thanks for any help.
>
> Mitch Berkson

--

Ignacio Rodriguez Ramirez de Arellano
Unidad de RMN
Universidad Complutense
Paseo Juan XXIII, 1
Madrid 28040, Spain

Tel. 34-91-394-3288
Fax  34-91-394-3245
e-mail: ignacio at sgirmn.pluri.ucm.es





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