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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
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