Working complex fractions without conjugate method

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Homework Help Overview

The discussion revolves around evaluating a complex fraction expression involving the subtraction of two fractions with complex numbers in the denominators. The original poster is required to provide the answer in polar form while avoiding the use of the complex conjugate method.

Discussion Character

  • Exploratory, Assumption checking, Problem interpretation

Approaches and Questions Raised

  • Participants explore the implications of using the complex conjugate method versus normal addition and subtraction of fractions. The original poster questions the starting point for the problem and considers alternative methods, including direct conversion to polar form.

Discussion Status

Some participants have offered insights into the meaning of "normal addition/subtraction of fractions," suggesting finding a common denominator. There is an ongoing exploration of how to approach the problem without relying on the complex conjugate method, with various interpretations being discussed.

Contextual Notes

The problem explicitly states that the complex conjugate method should not be used, which raises questions about the constraints of the solution approach. The original poster expresses uncertainty about the correct starting point and the implications of different methods.

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Homework Statement


Ive been given a question that requires an answer in polar form but the method I must use is the normal addition/subtraction of fractions. This throws me because I'm sure there is a simple method for the reciprocal of a complex number.

Q. 1/(13- 5i) - 1/(2-3i)

Homework Equations



where z = a + bi
i'm aware of how to change to polar for whole numbers and how to get where I want using the conjugate method but can't fathom the correct start point.


The Attempt at a Solution



I considered 1/13 - 1/5i using the rules of fractions but wasn't convinced.
The alternative was to convert straight to polar using 1 / 0degrees over the (13-5i in polar form)
 
Last edited:
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\frac{1}{a+ bi}= \frac{1}{a+ bi}\frac{a- bi}{a- bi}= \frac{a- bi}{(a+ bi)(a- bi)}
= \frac{a- bi}{a^2-b^2i^2}= \frac{a- bi}{a^2+ b^2}

(Even for real numbers,
\frac{1}{a+ b}\ne \frac{1}{a}+ \frac{1}{b})
 
Doesn't that just proove the Complex Conjugate method? I can only solve the answer without the use of this method.

The actual wording of the question is:
Evaluate the following expression using normal addition/subtraction of fractions and/or polar form (i.e DO NOT use the complex conjugate method) giving the result in polar form.

if I use (a-bi)/(a2 + b2) doesn't this just mean I've used the complex Conjugate Method? Or ar you saying I can do it this way:

where a^2 + b^2 = 13^2 + 5^2 = 194

13/194 + (5/194)i

0.067 + 0.026i
and the same for the second rectangular element of the question (1/(2-3i)
 
Welcome to PF.

I think "normal addition/subtraction of fractions" means you find a common denominator for the two fractions, and then you can add the resulting numerators.
 

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