Natural log of a complex number.

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Discussion Overview

The discussion revolves around evaluating the logarithms of complex numbers, specifically $\ln(1)$, $\text{Ln}(1)$, $\ln(3-j4)$, and $\text{Ln}(3-j4)$. Participants express confusion about the application of the logarithmic formula for complex numbers and the differences between the notations $\ln$ and $\text{Ln}$.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • Some participants note that the logarithm of a complex number $z$ can be expressed as $\ln z = \ln|z| + \text{arg}\, z$, but they struggle with applying this to specific examples.
  • One participant suggests that evaluating $\ln(1)$ is straightforward, implying that it should be easy to compute.
  • Another participant questions the difference between the notations $\ln a$ and $\text{Ln} a$, indicating a need for clarification on their meanings in the context of complex variables.
  • A later reply states that $\text{Ln} z$ represents the principal value of $\ln z$, suggesting a relationship between the two notations.
  • It is mentioned that $\ln z = \text{Ln} z + 2k\pi i$, indicating that there are multiple values for the logarithm of a complex number depending on the branch cut.

Areas of Agreement / Disagreement

Participants express uncertainty and confusion regarding the application of the logarithmic formula for complex numbers. There is no consensus on how to proceed with the evaluations, and the differences between the notations $\ln$ and $\text{Ln}$ remain a point of contention.

Contextual Notes

Participants have not resolved the mathematical steps necessary to evaluate the logarithms, and there are unresolved assumptions regarding the definitions and implications of the notations used.

Drain Brain
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Evaluate the following logarithms, expressing the answers in rectangular form

a. $\ln1$, $Ln1$
b. $\ln(3-j4)$, $Ln(3-j4)$

I know that the log of a complex number z is given as

$\ln z=\ln|z|+argz$

but I still don't know how to use this fact to solve the problems above. I'm having a hard time understanding the material that I read about this. please enlighten me.
 
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Drain Brain said:
Evaluate the following logarithms, expressing the answers in rectangular form

a. $\ln1$, $Ln1$
b. $\ln(3-j4)$, $Ln(3-j4)$

I know that the log of a complex number z is given as

$\ln z=\ln|z|+argz$

but I still don't know how to use this fact to solve the problems above. I'm having a hard time understanding the material that I read about this. please enlighten me.

Just a Question: what is the difference in the notations $\ln\ a$ and $\text{Ln}\ a$, being a a complex variable? ...

Kind regards

$\chi$ $\sigma$

- - - Updated - - -

Drain Brain said:
Evaluate the following logarithms, expressing the answers in rectangular form$\ln z=\ln|z|+arg z$

What I remember is that, setting $\displaystyle j = \sqrt{-1}$, is $\displaystyle \ln z = \ln |z| + j\ \text{arg}\ z$...

Kind regards

$\chi$ $\sigma$
 
Drain Brain said:
Evaluate the following logarithms, expressing the answers in rectangular form

a. $\ln1$, $Ln1$
b. $\ln(3-j4)$, $Ln(3-j4)$

I know that the log of a complex number z is given as

$\ln z=\ln|z|+argz$

but I still don't know how to use this fact to solve the problems above. I'm having a hard time understanding the material that I read about this. please enlighten me.

Surely you can do ln(1) with your eyes closed.

As for the rest, can't you evaluate |3 - 4j| and arg(3 - 4j) ?
 
chisigma said:
Just a Question: what is the difference in the notations $\ln\ a$ and $\text{Ln}\ a$, being a a complex variable? ...

Kind regards

$\chi$ $\sigma$

- - - Updated - - -
What I remember is that, setting $\displaystyle j = \sqrt{-1}$, is $\displaystyle \ln z = \ln |z| + j\ \text{arg}\ z$...

Kind regards

$\chi$ $\sigma$

the $Ln z$ is the principal value of $\ln z$
 
Drain Brain said:
the $Ln z$ is the principal value of $\ln z$

That means that is $\displaystyle \ln z = \text{Ln}\ z + 2\ k\ \pi\ i$... so that if you know you have the other one automatically... all right?...

Kind regards

$\chi$ $\sigma$
 

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