If z = -3+4i....(related vectors)

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Discussion Overview

The discussion revolves around the properties and calculations related to the complex number z = -3 + 4i. Participants explore various related complex numbers, including its vector representation, magnitude, and operations such as division by z and its conjugate. The scope includes mathematical reasoning and conceptual clarification regarding complex numbers.

Discussion Character

  • Mathematical reasoning
  • Conceptual clarification
  • Homework-related

Main Points Raised

  • Some participants question whether z can be considered a vector, noting a line above it that may indicate a conjugate.
  • Others clarify that the line over a complex number refers to its conjugate, defined as $\overline{z} = a - bi$.
  • There is a discussion about the magnitude of z, with participants confirming that $|z|$ represents the magnitude calculated as $|z| = \sqrt{a^2 + b^2}$.
  • One participant calculates the magnitude of z as 5 and questions if dividing 1 by z is equivalent to dividing by its magnitude.
  • Another participant provides a detailed calculation for $\frac{1}{z}$, demonstrating the process of multiplying by the conjugate to simplify the expression.
  • There is a correction regarding a misunderstanding about dividing by the magnitude versus dividing by z itself.

Areas of Agreement / Disagreement

Participants generally agree on the definitions and properties of complex numbers, such as the conjugate and magnitude. However, there remains some uncertainty regarding the interpretation of z as a vector and the implications of dividing by z versus its magnitude.

Contextual Notes

Some participants express uncertainty about the notation and properties of complex numbers, indicating a need for further clarification on related concepts.

Who May Find This Useful

This discussion may be useful for individuals learning about complex numbers, their properties, and operations, particularly in a mathematical or engineering context.

Raerin
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If z = -3+4i, determine the following related complex numbers

a) vector z
b) 3(vector z)
c) 1/z
d) 1/(vector z)
e) |z|
f) |vector z|
g) (vector z)/(|z|^2)

I'm not sure if it's a vector, but the z has a short line above it when I say "vector z."
 
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Re: If z = -3+4i...

The line over a complex number refers to its conjugate. If $z=a+bi$, then $\overline{z}=a-bi$. Are you familiar with the other notations?
 
Re: If z = -3+4i...

MarkFL said:
The line over a complex number refers to its conjugate. If $z=a+bi$, then $\overline{z}=a-bi$. Are you familiar with the other notations?
Nope :( but |z| refers to the length of it? So it'll be the radius of a circle?
 
Re: If z = -3+4i...

Yes, $|z|$ refers to the magnitude, which is given by:

$$|z|=\sqrt{a^2+b^2}$$

So, what do you find for the magnitude of the given complex number?
 
Re: If z = -3+4i...

MarkFL said:
Yes, $|z|$ refers to the magnitude, which is given by:

$$|z|=\sqrt{a^2+b^2}$$

So, what do you find for the magnitude of the given complex number?

Ahh, I see, so |z| would be 5.

Also, when 1 is divided by z, is it the same as dividing 1 with...5, let's say?
 
Re: If z = -3+4i...

Yes, correct on both counts. (Sun)

So, what about parts b) and c)?
 
Re: If z = -3+4i...

MarkFL said:
Yes, correct on both counts. (Sun)

So, what about parts b) and c)?

Okay, I understand everything now. Thanks for your help!
 
Re: If z = -3+4i...

Hi Raerin, welcome to MHB! :)

Raerin said:
Also, when 1 is divided by z, is it the same as dividing 1 with...5, let's say?

I'd like to add a bit of nuance here.

\begin{aligned}
\frac 1 z &= \frac 1 {-3+4i} \\
&= \frac 1 {-3+4i} \cdot \frac {-3-4i} {-3-4i} \\
&= \frac {-3-4i} {(-3+4i)(-3-4i)} \\
&= \frac {-3-4i}{(-3)^2-(4i)^2} \\
&= \frac {-3-4i}{9+16} \\
&= \frac 1 {25} (-3-4i)
\end{aligned}
 
Re: If z = -3+4i...

I like Serena said:
Hi Raerin, welcome to MHB! :)
I'd like to add a bit of nuance here.

\begin{aligned}
\frac 1 z &= \frac 1 {-3+4i} \\
&= \frac 1 {-3+4i} \cdot \frac {-3-4i} {-3-4i} \\
&= \frac {-3+4i} {(-3+4i)(-3-4i)} \\
&= \frac {-3-4i}{(-3)^2-(4i)^2} \\
&= \frac {-3-4i}{9+16} \\
&= \frac 1 {25} (-3-4i)
\end{aligned}

Yes, I was mistakenly referring to $$\frac{1}{|z|}$$. Good catch! (Yes)
 

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