       Re: Integration Problem

• To: mathgroup at smc.vnet.net
• Subject: [mg102022] Re: [mg102004] Integration Problem
• From: Bob Hanlon <hanlonr at cox.net>
• Date: Mon, 27 Jul 2009 05:52:57 -0400 (EDT)

```The problem arises with the use of inexact numbers in the exponent while trying to do exact integration

Integrate[Sqrt[(2 Exp[2*m])^2 + (1.5 Exp[1.5*m])^2], {m, 1, 2}]

79.6261

Using purely numerical

NIntegrate[Sqrt[(2 Exp[2*m])^2 + (1.5 Exp[1.5*m])^2], {m, 1, 2}]

49.7621

Or using exact exponents

N[Integrate[Sqrt[(2 Exp[2*m])^2 + (3/2 Exp[3/2*m])^2], {m, 1, 2}]]

49.7621

Bob Hanlon

---- JerrySpock <liquidsolids at hotmail.com> wrote:

=============
Hello, everyone.

I'm having a problem integrating to find an arc length.

I have two parametric equations:

x=e^(2t)

and

y=e^(1.5t)

I'm looking for the arc length from 1 to 2.

N[
Integrate[
Sqrt[
(2Exp[2*m])^2 + (1.5Exp[1.5*m])^2
],{m, 1, 2}]]

I keep getting the answer 79.6, but my TI-83 says the answer is 49.8.  I've been playing with this for hours, and I can't get it to work.  Any ideas what I'm doing wrong?

[Edited by: admin on Jul 25, 2009 7:22 AM]

```

• Prev by Date: Re: Integration Problem
• Next by Date: Re: How do you take apart a sequence?
• Previous by thread: Re: Integration Problem
• Next by thread: Re: Integration Problem