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MathGroup Archive 1999

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Re: Re: Mathematica can't win against Tiger Woods

  • To: mathgroup at smc.vnet.net
  • Subject: [mg19810] Re: [mg19765] Re: [mg19677] Mathematica can't win against Tiger Woods
  • From: BobHanlon at aol.com
  • Date: Fri, 17 Sep 1999 01:36:53 -0400
  • Sender: owner-wri-mathgroup at wolfram.com

Leszek,

soln1 = Solve[{p == b^2/a, e == Sqrt[a^2 - b^2]/a}, {a, b}];

Since you know that b > 0,

soln = Select[soln1, Simplify[(b /. #) > 0, {p > 0, 0 <= e < 1}] &] // 
      Flatten;
soln // InputForm

{b -> (I*p)/Sqrt[-1 + e^2], a -> -(p/(-1 + e^2))}

Look at the FullForm of the expression for b

FullForm[b /. soln]

Times[Complex[0, 1], Power[Plus[-1, Power[e, 2]], Rational[-1, 2]], p]

Replace the form that you want changed

soln /. Power[x_, Rational[-1, 2]] :> 
      -I*Power[-x, Rational[-1, 2]] // InputForm

{b -> p/Sqrt[1 - e^2], a -> -(p/(-1 + e^2))}

I would rather explain the concept of I to a high school class than 
semi-latus rectum.

Bob Hanlon


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