Re: Q: Solve gives complex solution where there is a noncomplex solution how to get the last one?

*To*: mathgroup at smc.vnet.net*Subject*: [mg50322] Re: [mg50300] Q: Solve gives complex solution where there is a noncomplex solution how to get the last one?*From*: Murray Eisenberg <murray at math.umass.edu>*Date*: Fri, 27 Aug 2004 02:57:44 -0400 (EDT)*Organization*: Mathematics & Statistics, Univ. of Mass./Amherst*References*: <200408261050.GAA16310@smc.vnet.net>*Reply-to*: murray at math.umass.edu*Sender*: owner-wri-mathgroup at wolfram.com

You used approximate (machine) numbers in the equation, namely, the exponent, so you got machine numbers in your answer. But: Solve[x y/Sqrt[1 + y^2] == a, y] // InputForm {{y -> -(a/Sqrt[-a^2 + x^2])}, {y -> a/Sqrt[-a^2 + x^2]}} (I'm using InputForm on the result of Solve just to obtain the answer in a linear form suitable for e-mail rather than Mathematica's default 2D StandardForm.) Dick Barends wrote: > Hello, > > The following line > > Solve[x y / ( 1 + y^2 )^0.5 == a, y] > > Gives a complex solution : (0.+ i )a / (a^2 - x^2)^0.5 > Which is correct but could be simpler, not complex > > The solution I expected is: a/(x^2 - a^2)^0.5 > > How can I instruct Mathematica (Solve) to give the simple solution directly. > > kind regards > Dick Barends > > > -- Murray Eisenberg murray at math.umass.edu Mathematics & Statistics Dept. Lederle Graduate Research Tower phone 413 549-1020 (H) University of Massachusetts 413 545-2859 (W) 710 North Pleasant Street fax 413 545-1801 Amherst, MA 01003-9305

**References**:**Q: Solve gives complex solution where there is a noncomplex solution how to get the last one?***From:*"Dick Barends" <dick.barends@wxs.nl>