MathGroup Archive 2001

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Integration by substitution

  • To: mathgroup at
  • Subject: [mg29800] Integration by substitution
  • From: ggarrett7 at (G. A. Garrett)
  • Date: Tue, 10 Jul 2001 20:25:36 -0400 (EDT)
  • Sender: owner-wri-mathgroup at

I was wondering if someone could explain to me why the first input
below gives no answer while the second input does. It never crossed my
mind the Mathematica wouldn't have seen the simple substitution of
sp=s/a that produced an answer. I am running ver. 4.0 in a Windows
environment. I am basically looking for a characteristic that I can be
on the look out for in the future.

Integrate[Sech[s/a]^2 Sech[(t - s)/a]^2, {s, -Infinity, Infinity}]

Integrate[a Sech[sp]^2 Sech[(tp - sp)]^2, {sp, -Infinity, Infinity}]

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