       Re: Simply derivative question, Math 5.

• To: mathgroup at smc.vnet.net
• Subject: [mg50246] Re: [mg50240] Simply derivative question, Math 5.
• From: DrBob <drbob at bigfoot.com>
• Date: Mon, 23 Aug 2004 06:34:07 -0400 (EDT)
• References: <200408220419.AAA10290@smc.vnet.net>
• Sender: owner-wri-mathgroup at wolfram.com

```Both these answers are correct:

D[(1 + c*E^t)/(1 - c*E^t), t]

(c*E^t)/(1 - c*E^t) + (c*E^t*(1 + c*E^t))/(1 - c*E^t)^2

D[(1 + c*e^t)/(1 - c*e^t), t]

(c*e^t*Log[e])/(1 - c*e^t) + (c*e^t*(1 + c*e^t)*Log[e])/(1 - c*e^t)^2

Built-in constants start with capitals; hence e is undefined (unless you define it).

Bobby

On Sun, 22 Aug 2004 00:19:51 -0400 (EDT), Ted Kahn <tedkahn at mindspring.com> wrote:

> Hello- I am trying to take the derivative of the following function:
>
> (1 + c*e^t)/(1 - c*e^t)
>
> with respect to t.
>
> ================
> \!\(Simplify[D[\(1 + c\ e\^t\)\/\(1 - c\ e\^t\), t]]\)
> ============
>
> The answer I get includes an "extra" Log[e] in the numerator. Am I not
> using the program correctly or am I not understanding the answer
> correctly? Other?
>
> thanks, -ted

--
DrBob at bigfoot.com
www.eclecticdreams.net

```

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