Exact 3rd degree poly root

02262016, 05:40 AM
Post: #1




Exact 3rd degree poly root
Is there a way to get an exact instead of decimal root to a 3rd degree polynomial such as
X^3  (21\4)*x^2 + 9*x  4 ? My Classpad 400 can accomplish this. How do I do so on the Prime? 

02262016, 10:00 AM
Post: #2




RE: Exact 3rd degree poly root
You must make a program if you want a solution expressed in terms of radicals. You can inspire yourself from the following Xcas program:
Code:


02262016, 03:38 PM
(This post was last modified: 02262016 03:45 PM by rhab.)
Post: #3




RE: Exact 3rd degree poly root
Maxima can do that by default:
solve(x^3  (21/4)*x^2 + 9*x  4=0, x); You can try it online with http://maximaonline.org/#?in=solve(x%5E...B%0A%20%09 BTW, you can install maxima on your phone! 

02262016, 07:45 PM
Post: #4




RE: Exact 3rd degree poly root
Yes, but I think you did not understand what I wrote. It's nice to impress your friends with the root expressions with nested radicals, but after that you won't be able to simplify expressions easily. For example, it will probably be costly to find the value of the product of the three roots.
And by the way, there is an experimental version of Xcas that runs on your phone or tablet or any browser (Firefox recommended) Xcas online offline. Once downloaded, all computations are done on your phone, tablet or PC, you don't need an Internet connection anymore. 

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