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Re: Real Solutions

  • To: mathgroup at smc.vnet.net
  • Subject: [mg95830] Re: Real Solutions
  • From: dimitris <dimmechan at yahoo.com>
  • Date: Wed, 28 Jan 2009 06:31:19 -0500 (EST)
  • References: <glmssi$mkr$1@smc.vnet.net>

On 27 =CE=99=CE=B1=CE=BD, 13:58, Kowalczyk-Schr=C3=B6der wrote:
> Hi,
> I need only the real solutions from Solve or NSolve. I found a
> complicated way with a lot of "ifs" to get, what I want. Is there an
> easier way to do this? (I don't want to use Reduce.)
> Regards
> J.Schroeder

Something like
In[75]:=
x /. Solve[x^4 + x^3 + x^2 + 2*x + 1 == 0, x]
Select[%,Element[#,Reals] & ]

Out[75]=
{-1, -(2/(3*(-9 + Sqrt[93])))^(1/3) + ((1/2)*(-9 + Sqrt[93]))^(1/3)/3^
(2/3),
  -(((1 + I*Sqrt[3])*((1/2)*(-9 + Sqrt[93]))^(1/3))/(2*3^(2/3))) + (1
- I*Sqrt[3])/(2^(2/3)*(3*(-9 + Sqrt[93]))^(1/3)),
  -(((1 - I*Sqrt[3])*((1/2)*(-9 + Sqrt[93]))^(1/3))/(2*3^(2/3))) + (1
+ I*Sqrt[3])/(2^(2/3)*(3*(-9 + Sqrt[93]))^(1/3))}

Out[76]=
{-1, -(2/(3*(-9 + Sqrt[93])))^(1/3) + ((1/2)*(-9 + Sqrt[93]))^(1/3)/3^
(2/3)}



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