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Re: Sqrt of complex number

  • To: mathgroup at smc.vnet.net
  • Subject: [mg126642] Re: Sqrt of complex number
  • From: "Dave Snead" <dsnead6 at charter.net>
  • Date: Mon, 28 May 2012 05:10:39 -0400 (EDT)
  • Delivered-to: l-mathgroup@mail-archive0.wolfram.com
  • References: <201205270842.EAA17817@smc.vnet.net>

Use Solve to get both answers:

Solve[z^2==3-4I,z]

{{z->-2+I},{z->2-I}}

Cheers,
Dave Snead


-----Original Message----- 
From: Jacare Omoplata
Sent: Sunday, May 27, 2012 1:42 AM
To: mathgroup at smc.vnet.net
Subject: [mg126642] Sqrt of complex number

Hi,

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

Why does Mathematica give the first answer and not the second? Does it 
choose the answer with the positive real number? Is there any way I can get 
both answers? Or do I just have to remember that the negative of the given 
answer is also an answer?

Thanks.





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