When I use the D() operator on a MathObject formula involving exponentials of the form "e^x" instead of "exp(x)", the differentiation rule uses the general base rule: d/dx[b^x] = b^x ln(b). Consequently, when I "Show correct answers" on a problem, it always shows a factor ln(e).

Is there an easy way to make this go away?

- Brian

D. Brian Walton

James Madison University

### ln(e) and MathObject differentiation

by D. Brian Walton -
In reply to D. Brian Walton
Tuesday, 26 July 2011, 2:32 PM

### Re: ln(e) and MathObject differentiation

by Arnold Pizer -
Hi Brian,

I'm not sure if there is an easy way to make this go away, but if you do not like the way MathObjects format an answer (things like the derivative of e^x or x^x come to mind), you can always specify things the way you want. E.g.

$a = random(2,7,1);

$f = Compute("e^{${a}x}");

$ans = Compute("${a}e^{${a}x}");

###################################

# Main text

Context()->texStrings;

BEGIN_TEXT

Let \( f(x) = \displaystyle $f \). Find \(f'(x)\).

$PAR

\(f'(x) =\) \{ans_rule(50) \}

END_TEXT

Context()->normalStrings;

###################################

# Answers

$showPartialCorrectAnswers = 1;

#$ans=$f->D('x');

ANS($ans->cmp);

Arnie

In reply to Arnold Pizer
Tuesday, 26 July 2011, 2:52 PM

### Re: ln(e) and MathObject differentiation

by D. Brian Walton -
Yes, I suppose you are right. But that was the whole point in using MathObjects to begin with, so that I could avoid worrying about thinking through the rules when constructing the answer. (Of course, I also recognize that MathObjects does not do any algebra to simplify the answer, so maybe this is the approach I will want to take.)

- Brian

- Brian