Drexel dragonThe Math ForumDonate to the Math Forum

Search All of the Math Forum:

Views expressed in these public forums are not endorsed by Drexel University or The Math Forum.

Math Forum » Discussions » Inactive » k12.ed.math

Topic: Questions regarding Descartes's Rule of Signs
Replies: 2   Last Post: Feb 16, 2005 12:21 AM

Advanced Search

Back to Topic List Back to Topic List Jump to Tree View Jump to Tree View   Messages: [ Previous | Next ]

Posts: 3
Registered: 1/29/05
Questions regarding Descartes's Rule of Signs
Posted: Feb 15, 2005 4:48 PM
  Click to see the message monospaced in plain text Plain Text   Click to reply to this topic Reply

Hello. I'm working with Descartes's rule of signs currently and I
understand it, however this equation doesn't follow the rule. Are there

- Find all real zeros
f(x) = 2x^3 + 3x^2 - 1
f(-x) = 2(-x)^3 + 3(-x)^2 - 1

In this equation I see 1 sign change. Using Descartes's rule this would
show 1 or 0 real zero's with no negative zero's.

However! There is 1 positive zero (1/2) and 1 negative zero (-1).

Can somebody please explain to me what I am doing wrong with the rule?


submissions: post to k12.ed.math or e-mail to k12math@k12groups.org
private e-mail to the k12.ed.math moderator: kem-moderator@k12groups.org
newsgroup website: http://www.thinkspot.net/k12math/
newsgroup charter: http://www.thinkspot.net/k12math/charter.html

Point your RSS reader here for a feed of the latest messages in this topic.

[Privacy Policy] [Terms of Use]

© The Math Forum 1994-2015. All Rights Reserved.