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John Jones - Roots in student answers

John Jones - Roots in student answers

by Arnold Pizer -
Number of replies: 0
inactiveTopicRoots in student answers topic started 10/16/2003; 3:30:14 PM
last post 10/16/2003; 9:58:09 PM
userJohn Jones - Roots in student answers  blueArrow
10/16/2003; 3:30:14 PM (reads: 677, responses: 1)

We had a problem for students to find real roots of

  x^6 + x^3 - 3
The positive root is fine. If a student enters the negative root as
((-1 - sqrt(13))/2)^(1/3)
then WW produces a pink screen. The answer itself is reasonable for this question.

Ultimately it is because WW passes the evaluation of this to perl, and perl computes the exponential by first taking ln of the (negative) base.

Fixing this looks hard, but it is worth thinking about. It is a case where students can correctly complain that WW won't accept their correct answer.


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userMichael Gage - Re: Roots in student answers  blueArrow
10/16/2003; 9:58:09 PM (reads: 869, responses: 0)
Hi John,

Short of writing our own compiler I don't see how to fix this behavior either. I have run into it before and I fixed it "in the documentation". That is, I warned students about the problems of taking roots of negative numbers and how it was actually done on computers using logs. It was a calculus class, so they were actually reasonably interested in how computers calculated such things.

My guess is that a pocket calculator wouldn't do any better on this answer, but I haven't tried it recently.


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