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

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aaronhunter@gmail.com

Posts: 3
Registered: 1/29/05
Questions regarding Descartes's Rule of Signs
Posted: Feb 15, 2005 4:48 PM
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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
exceptions?

- 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?

Thanks!
-Aaron


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