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