Finding a Complex Number Given Arg and Modulus

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Homework Help Overview

The problem involves finding a complex number \( w \) given its argument and modulus. Specifically, the argument is \( \frac{\pi}{4} \) and the modulus is derived from the expression \( |w \cdot \bar{w}| = 20 \).

Discussion Character

  • Exploratory, Assumption checking

Approaches and Questions Raised

  • Participants discuss the implications of the argument on the form of \( w \), suggesting that if \( \text{arg}(w) = \frac{\pi}{4} \), then \( a \) and \( b \) must be equal. There is also a consideration of the signs of \( a \) and \( b \) and how they affect the argument.

Discussion Status

The discussion includes attempts to determine the values of \( a \) and \( b \) based on the given conditions. Some participants express agreement on certain points, while others question the validity of negative values for \( a \) and \( b \) in relation to the argument's quadrant.

Contextual Notes

There is a focus on the implications of the quadrant in which the complex number lies, particularly regarding the argument when both components are negative. The discussion reflects on the constraints imposed by the argument and modulus without reaching a definitive conclusion.

squenshl
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Homework Statement


If ##\text{arg}(w)=\frac{\pi}{4}## and ##|w\cdot \bar{w}|=20##, then what is ##w## of the form ##a+bi##.

Homework Equations

The Attempt at a Solution


The only way for the argument of ##w## to be ##\frac{\pi}{4}## is when ##a+bi## where ##a=b \in \mathbb{Z}## right?
 
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That is correct.
 
andrewkirk said:
That is correct.
Great thanks.
I get ##a=b= \pm\sqrt{10}## so ##w## follows.
 
squenshl said:
Great thanks.
I get ##a=b= \pm\sqrt{10}## so ##w## follows.

No, ##a = b = -\sqrt{10}## would not be correct; only the ##+\sqrt{10}## answer applies.
 
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Ray Vickson said:
No, ##a = b = -\sqrt{10}## would not be correct; only the ##+\sqrt{10}## answer applies.

Do you understand Ray's point? What is ##\arg(w)## if ##a = b## and both are negative?
 
RPinPA said:
Do you understand Ray's point? What is ##\arg(w)## if ##a = b## and both are negative?
I do.
##w=-\sqrt{10}-\sqrt{10}i## is in the wrong quadrant.
##\text{arg}(w)=-\pi+\frac{\pi}{4}##.
 

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