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Re: Sqrt of complex number
*To*: mathgroup at smc.vnet.net
*Subject*: [mg126652] Re: Sqrt of complex number
*From*: David Bailey <dave at removedbailey.co.uk>
*Date*: Tue, 29 May 2012 05:45:27 -0400 (EDT)
*Delivered-to*: l-mathgroup@mail-archive0.wolfram.com
*References*: <201205270842.EAA17817@smc.vnet.net> <jpvfh3$q6g$1@smc.vnet.net>
>
> When I try to find the square root of of a complex number, I get only one
> answer.
>
> In[1]:= Sqrt[3-4 I]
> Out[1]= 2-I
>
> But -2+I is an answer as well.
>
> In[2]:= (-2+I)^2
> Out[2]= 3-4 I
>
In addition to what others have said, it is maybe worth pointing out
that in general, the Sqrt expression would be embedded in a larger
expression, such as a+Sqrt[3-4 I]+42 - so what should Mathematica do? If
it returns a list of all possible answers, that might not be acceptable
to something that was expecting a single value, and anyway, expressions
such as ArcSin[.2] would have an infinite number of answers!
The only possible alternative strategy would be not to evaluate at all,
as is the case with Sqrt[x^2] (since the answer can by x or -x).
David Bailey
http://www.dbaileyconsultancy.co.uk
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