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Re: unwanted Complex result

  • To: mathgroup at smc.vnet.net
  • Subject: [mg91596] Re: [mg91589] unwanted Complex result
  • From: Bob Hanlon <hanlonr at cox.net>
  • Date: Thu, 28 Aug 2008 07:39:27 -0400 (EDT)
  • Reply-to: hanlonr at cox.net

soln = Solve[(Sqrt[speed^2 - windx^2] + windy)/a 
      speed^2 + b speed + c == distance/height, speed];

Select[soln /.
   {windx -> 1, windy -> 1, a -> 1, b -> 1, c -> 1,
    distance -> 20, height -> 5} // N,
 FreeQ[#, Complex] &]

{{speed->-1.46762},{speed->1.11901}}


Bob Hanlon

---- John Rivers <first10 at btinternet.com> wrote: 

=============
Solve[
(Sqrt[speed ^ 2 - windx ^ 2] + windy) / a speed ^ 2 + b speed + c ==
distance / height
, speed]

this works but returns 4 solutions that all return complex numbers

I need a real number

how do I:

- convert a complex result into real number
or
- solve the equation to give only real numbers





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