Re: Roots selection
- To: mathgroup at smc.vnet.net
- Subject: [mg43013] Re: Roots selection
- From: Paul Abbott <paul at physics.uwa.edu.au>
- Date: Fri, 8 Aug 2003 00:26:27 -0400 (EDT)
- Organization: The University of Western Australia
- References: <bgqa9u$dae$1@smc.vnet.net>
- Sender: owner-wri-mathgroup at wolfram.com
In article <bgqa9u$dae$1 at smc.vnet.net>, akhmel at hotmail.com (Alex) wrote: > I am solving a cubic equation and I got 3 roots. How can select root > number 2 for processing? Using Cardano's formula for the roots of a cubic is usually a waste of time; working with Root objects is more valuable. SetOptions[Roots, Cubics -> False, Quartics -> False]; Then you can select root 2 as suggested by others, x /. Solve[x^3 + b x^2 + c x + d == 0, x][[2]] and work with this object. For example, D[%, b] // FullSimplify gives a simple analytic expression for this derivative. Cheers, Paul -- Paul Abbott Phone: +61 8 9380 2734 School of Physics, M013 Fax: +61 8 9380 1014 The University of Western Australia (CRICOS Provider No 00126G) 35 Stirling Highway Crawley WA 6009 mailto:paul at physics.uwa.edu.au AUSTRALIA http://physics.uwa.edu.au/~paul