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MathGroup Archive 2006

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Re: Selecting Real Roots, Again

  • To: mathgroup at smc.vnet.net
  • Subject: [mg67174] Re: Selecting Real Roots, Again
  • From: David Bailey <dave at Remove_Thisdbailey.co.uk>
  • Date: Sun, 11 Jun 2006 02:18:10 -0400 (EDT)
  • References: <e6b5q5$d3c$1@smc.vnet.net>
  • Sender: owner-wri-mathgroup at wolfram.com

Hello,

If you execute Solve[.9 x^10 + .1 x^2 ==y,x] you get a set of Root 
expressions because beyond order 4 symbolic polynomial equations such as 
this do not have solutions (except in terms of some impossibly 
complicated expressions involving Hypergeometrics or Theta functions). 
See for example:

http://library.wolfram.com/examples/quintic/main.html

Given that you don't have any answers, I can't see how you can filter 
them to select the Real ones!

Note that you could, of course, solve this equation numerically if you 
gave y a value - then you could use the methods previously discussed to 
eliminate the imaginary roots.

David Bailey
http://www.dbaileyconsultancy.co.uk


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