Dividing/Multiplying Imaginary Numbers

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Discussion Overview

The discussion focuses on the methods for multiplying and dividing imaginary numbers, particularly in the context of AC circuit calculations. Participants explore the convenience of different approaches, including the use of phasors and complex conjugates, while expressing frustrations with the complexity of these calculations.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant questions whether there is a more convenient method for multiplying and dividing imaginary numbers than converting to and from phasors, especially when adding and subtracting.
  • Another participant suggests rationalizing the denominator as a potential method, although they acknowledge the terminology may not be precise.
  • A different participant mentions the use of complex conjugates for division in Cartesian form, noting that this can be tedious with multiple impedances.
  • It is pointed out that dividing complex numbers can also be done in polar form by dividing magnitudes and subtracting angles.
  • One participant shares a technology-based solution using a TI-83+ calculator to perform the calculations, providing a specific example of the output.
  • Another participant confirms that polar form is equivalent to phasors and provides an example of how to express a complex number in this form.
  • One participant concludes that there is no simpler method available, expressing a desire for a new operation to ease the calculations.

Areas of Agreement / Disagreement

Participants express a lack of consensus on a simpler method for performing these calculations, with some agreeing on the use of complex conjugates and polar forms while others remain frustrated with the existing methods.

Contextual Notes

Some limitations are noted, such as the tediousness of calculations with multiple impedances and the reliance on specific forms (Cartesian vs. polar) for division methods.

cstoos
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Is there a more convenient way to multiply and divide imaginary numbers than converting back and forth from phasors? (I guess I should say "when also having to add and subtract them")

I always find AC circuit calculations to be tedious and problem filled when I do it that way.

For example if I had to simplify something like:



(6+j3)/(6+j8)+(5+j9)/(2+j7)
 
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Have you tried rationalizing the denominator? (I suppose "rationalize" is the wrong word here, but it's the same procedure)
 
I think you are referring to multiplying by the complex conjugate...correct? A possibility yet still tedious when dealing with say, three impedences in parallel.

There is no way to directly divide? Seems like there should be.

Oh, and the above problem is completely made up, so no, I haven't tried that. I was just using it as a visual referrence as to what I was talking about.
 
There are only two ways that I know about for dividing complex numbers. One way involves the complex conjugate for complex numbers in Cartesian form. The other way is to divide the magnitudes and subtract the arguments (angles) for complex numbers in polar form.
 
Mark44 said:
There are only two ways that I know about for dividing complex numbers. One way involves the complex conjugate for complex numbers in Cartesian form. The other way is to divide the magnitudes and subtract the arguments (angles) for complex numbers in polar form.
I believe the "polar form" is what cstoos is referring to as "phasors".
 
cstoos said:
Is there a more convenient way to multiply and divide imaginary numbers than converting back and forth from phasors? (I guess I should say "when also having to add and subtract them")...
(6+j3)/(6+j8)+(5+j9)/(2+j7)
Well, yes, there is technology!
On the TI-83+ (in a+ bi mode)
...
(6+3i)/(6+8i) + (5+9i)/(2+7i) (MATH-> FRAC)
=
524/265 - (329/530)i.
 
You and your fancy calculators...

And yes, HallsofIvy is correct in his statement. Polar form is the same a phasors.

For example 6+3i would be written 6.7/26.6


Well, I guess my question was answered. No simpler way to do it. Now one of you just needs to find a new operation that will make my life easier.
 

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