Re: Sqrt of complex number

*To*: mathgroup at smc.vnet.net*Subject*: [mg126643] Re: Sqrt of complex number*From*: Helen Read <readhpr at gmail.com>*Date*: Mon, 28 May 2012 05:11:00 -0400 (EDT)*Delivered-to*: l-mathgroup@mail-archive0.wolfram.com*References*: <jpspgr$hdj$1@smc.vnet.net>

If you ask for the square root, cube root, or 4th root etc., Mathematica will return the principal root. To get them all, use Solve. Solve[z^2 == 3 - 4 I, z] Solve[z^3 == -8, z] Solve[z^3 == -8, z] // ComplexExpand Helen Read University of Vermont On 5/27/2012 4:44 AM, Jacare Omoplata wrote: > 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. >