Re: Simply derivative question, Math 5.

*To*: mathgroup at smc.vnet.net*Subject*: [mg50257] Re: [mg50240] Simply derivative question, Math 5.*From*: Murray Eisenberg <murray at math.umass.edu>*Date*: Mon, 23 Aug 2004 06:34:25 -0400 (EDT)*Organization*: Mathematics & Statistics, Univ. of Mass./Amherst*References*: <200408220419.AAA10290@smc.vnet.net>*Reply-to*: murray at math.umass.edu*Sender*: owner-wri-mathgroup at wolfram.com

As the Mathematica Book (printed or electronic) explains, ALL built-in objects in Mathematica have names that begin with an upper-case letter. So the Napierian "e" is represented by E, not e. (Or, if you want it to look more like conventional mathematical notation, type Esc e Esc to obtain the Mathematica stylized e; in fact, you'll see that stylized e in the result.) So Mathematica was treating e as an unknown constant and gave the correct answer. When e = E, then Log[e] = 1, so no "extra" factor: D[(1 + c E^t)/(1 - c E^t), t] // Simplify By the way, you don't need an explicit multiplication operator after the c here -- just a space (so Mathematica can see you have two single-letter names rather than a two-letter name cE). It's REALLY worth a couple hours of your time to read the early material in the Mathematica Book! It will save you a lot of time avoiding such basic difficulties. Ted Kahn 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 -- Murray Eisenberg murray at math.umass.edu Mathematics & Statistics Dept. Lederle Graduate Research Tower phone 413 549-1020 (H) University of Massachusetts 413 545-2859 (W) 710 North Pleasant Street fax 413 545-1801 Amherst, MA 01003-9305

**Follow-Ups**:**Re: Re: Simply derivative question, Math 5.***From:*Murray Eisenberg <murray@math.umass.edu>

**References**:**Simply derivative question, Math 5.***From:*"Ted Kahn" <tedkahn@mindspring.com>