Puzzling results from CAS
01-27-2017, 05:14 PM
Post: #1
 KeithB Senior Member Posts: 363 Joined: Jan 2017
Puzzling results from CAS
I just saw this on the HP Prime forum, but it did not get an answer.

Trying to find the roots of this polynomial:
f(x) = x^4 - 3x^3 - 2.75x² + 12x - 5
which are 2.5, -2, 2, and 0.5.

Both proot() and zeros() return: 2.5, 2, -2 and 0.

Graphing it makes it very clear that the root is at 0.5 and nowhere near 0.

BTW, how do you enter the coefficients in proot()? I tried entering only the coefficients and got really weird results.
01-27-2017, 05:50 PM
Post: #2
 Tim Wessman Senior Member Posts: 2,284 Joined: Dec 2013
RE: Puzzling results from CAS
I'm guessing the approximate numbers in there are messing the cas up. If you enclose it in an exact() call to convert the decimal approximates to fractions then it works fine.

TW

Although I work for HP, the views and opinions I post here are my own.
01-27-2017, 06:02 PM (This post was last modified: 01-27-2017 06:04 PM by KeithB.)
Post: #3
 KeithB Senior Member Posts: 363 Joined: Jan 2017
RE: Puzzling results from CAS
Or just make the 2.75 11/4.

(I found my problem with the coefficients, I just entered them, I did not make them a vector.)

Thanks.
01-27-2017, 06:45 PM (This post was last modified: 01-27-2017 06:46 PM by Fortin.)
Post: #4
 Fortin Member Posts: 59 Joined: Jul 2015
RE: Puzzling results from CAS
The [a b/c] key will also enclose the last ans in exact(). It's very handy to be able to just press the fraction key when one needs fractions.
01-27-2017, 06:55 PM
Post: #5
 parisse Senior Member Posts: 1,243 Joined: Dec 2013
RE: Puzzling results from CAS
This bug was reported a few weeks ago, it is now fixed in the source code.
http://www-fourier.ujf-grenoble.fr/%7epa...%20-%205)&
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