Can Termwise Differentiation Be Applied to the Series Ʃ(2+3i)^(2+i)n?

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Discussion Overview

The discussion centers on the application of termwise differentiation to the series Ʃ(2+3i)^(2+i)n, exploring the implications of complex analysis and the nature of the summation variable.

Discussion Character

  • Debate/contested

Main Points Raised

  • One participant suggests differentiating the series with respect to n, proposing the result as Ʃ n(2+3i)^(2+i)n-1.
  • Another participant questions the ambiguity in the problem, asking for clarification on the summation variable and the nature of n (whether it is an integer or can be real or complex).
  • A third participant clarifies that the summation index is n, confirming that i is an imaginary number, and expresses uncertainty about the absence of a declared z in the problem.
  • A later reply states that the series can be represented as Σ r^n, with r = (2+3i)^(2+i), and notes that since |r| > 1, the series diverges, suggesting that defining it as a function may not be appropriate.

Areas of Agreement / Disagreement

Participants express differing views on the nature of the series and whether termwise differentiation can be applied, with no consensus reached on how to proceed given the divergence of the series.

Contextual Notes

There are limitations regarding the assumptions about the summation variable and the nature of n, as well as the implications of divergence on the ability to differentiate the series.

sgonzalez90
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Ʃ(2+3i)^(2+i)n

Since there is no declared z (complex analysis)
in this problem would we take this differentiation with respect to n?

If so, my answer was

Ʃ n(2+3i)^(2+i)n-1
 
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Your description of the problem is too ambiguous. What is your summation variable? Is it i or n? Or is i the imaginary number? And is n supposed to be in the power with (2+i)? Is n supposed to be an integer or can it be any number (real or complex)?
 
The summation index is n so 0 to inf and i is an imaginary number. In all the problems we have seen we are given z because z = x + iy, but here none is given..so I'm unsure if it should just be zero or if we should assume this is z^u or u^z? I'm not sure, the professor didn't specify.
 
[itex]= \Sigma r^{n}[/itex], with r = (2+3i)^(2+i), but |r| = 4.86... > 1 [itex]\Rightarrow[/itex] the sum diverges, so it doesn't even make sense to define it as a function (at least not in the traditional simple way). Therefore you can't take any derivative.
 

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