4th degree equations

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Asatur Khurshudyan
Asatur Khurshudyan il 18 Nov 2011
Hi, can anyone help me with this problem? We need the smallest positive real root of this equation
a*x^4+b*x^3+c*x^2+d*x+e=0,
where a>0, b<0, c>0, d<0 and e>0. As Descartes said, in that case this equation has at least 2 positive real roots.
Thank you for your attention.

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Walter Roberson
Walter Roberson il 18 Nov 2011
r = roots([a,b,c,d,e]);
r(imag(r)~=0) = []; %remove complex
r(r <= 0) = []; %remove non-positive
min(r) %now it is the smallest positive real root
  5 Commenti
Walter Roberson
Walter Roberson il 19 Nov 2011
I think I do not know enough polynomial theory to come up with a useful answer on this, sorry.
Asatur Khurshudyan
Asatur Khurshudyan il 20 Nov 2011
No, I mean with Matlab. If there exist exact method, than it must be done by mathlab, I suppose. All right, as you wish.

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