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MathGroup Archive 1995

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Re: Re (-1)^(3/4) -> (-1+I)/Sqrt[2] ?

  • To: mathgroup at christensen.cybernetics.net
  • Subject: [mg594] Re: [mg584] Re[mg557] (-1)^(3/4) -> (-1+I)/Sqrt[2] ?
  • From: karl at faepds01.tu-graz.ac.at (Karl Unterkofler)
  • Date: Thu, 23 Mar 1995 09:17:18 +0100

>> Does anybody know a core or standard package command that makes
>> transformations like  (-1)^(3/4) -> (-1+I)/Sqrt[2] ?
>
>There was a simple answer to my question, supplied by Robby Villegas of
>WRI.
>
>Here it is: ComplexExpand.
>
>I missed it because there is nothing like ComplexExpand[(-1)^(3/4)] among
>the examples given in The Book.  This is a really common need, and I hope
>it will appear as an example in future editions.

I tried

In[422]:= ComplexExpand[(-1)^(1/5)] // InputForm
Out[422]//InputForm=Cos[Pi/5] + I*Sin[Pi/5]

But  want I want is

Cos[ Pi/5] = (1+ Sqrt[5])/4

Any suggestions?

karl unterkofler




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