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Re: Exclude O[] from Series[] for Solve[] in Mathematica

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  • Subject: [mg92845] Re: Exclude O[] from Series[] for Solve[] in Mathematica
  • From: Alexei Boulbitch <Alexei.Boulbitch at>
  • Date: Wed, 15 Oct 2008 05:36:03 -0400 (EDT)

I expand a function as a Series[] but the O[] part prevents Solve[] from
working. I try Part[] and it returns something which also confuses
Solve[]. First[] works, but produces useless results, but this is why I am
sure this is what I want to do.

Hi, Vasos,
There is a function Normal[] that does the job. Compare:

In[5]:= Series[Sin[x], {x, 0, 5}]

Out[5]= (SeriesData[$CellContext`x, 0, {
 1, 0, Rational[-1, 6], 0, Rational[1, 120]}, 1, 6, 1])

with the following:

In[4]:= Normal[Series[Sin[x], {x, 0, 5}]]

Out[4]= x - x^3/6 + x^5/120

Check Help/Series for more details.

With this the Solve operator works:

In[7]:= Solve[Normal[Series[Sin[x], {x, 0, 5}]] == 0, x]

Out[7]= {{x -> 0}, {x -> -Sqrt[2 (5 - \[ImaginaryI] Sqrt[5])]}, {x -> 
   Sqrt[2 (5 - \[ImaginaryI] Sqrt[5])]}, {x -> -Sqrt[
    2 (5 + \[ImaginaryI] Sqrt[5])]}, {x -> Sqrt[
   2 (5 + \[ImaginaryI] Sqrt[5])]}}

Have success, Alexei

Alexei Boulbitch, Dr., Habil.
Senior Scientist

ZAE Weiergewan
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