Complex Analysis - Value of Arg[(z-1)/(z+1)] between -pi and pi

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The discussion revolves around finding the argument of the complex expression Arg[(z-1)/(z+1)] for points z on the unit circle. It is established that Arg[(z-1)/(z+1)] equals π/2 when the imaginary part of z is greater than zero and -π/2 when it is less than zero. Participants explore the calculation of the expression by converting it into a form that reveals its real and imaginary parts. The conversation highlights the importance of understanding the argument's geometric interpretation as the angle with the positive x-axis. Ultimately, the conclusion reinforces the relationship between the imaginary part of z and the resulting argument values.
  • #31
OK, now the \frac{2b}{2a+1} is just a real number, so we're dealing with a multiple of i.

So our value could be 3i, 4i, 6i or some other multiple of i. What is the argument of a multiple of i?
 
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  • #32
micromass said:
OK, now the \frac{2b}{2a+1} is just a real number, so we're dealing with a multiple of i.

So our value could be 3i, 4i, 6i or some other multiple of i. What is the argument of a multiple of i?

pi/2, right?
 
  • #33
cooljosh2k2 said:
pi/2, right?

Not really, because we can also have negative multiples. -i and -3i are also multiples.
 
  • #34
micromass said:
Not really, because we can also have negative multiples. -i and -3i are also multiples.

well, pi/2 for positive multiples of i or I am > 0, or -pi/2 for negative multiples of i, or I am < 0
 
  • #35
Indeed! That's it!
 
  • #36
micromass said:
Indeed! That's it!

WOW! Thank you so much for helping and putting up with me!
 

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