Analyze the Complex Function by using the Principal log Branch I am trying to analyze the function sqrt(1-z^2), where the square root function is defined by the principal branch of the log function. I want to locate the the discontinuities. I know the discontinuities will lie on the negative real axis but I cannot figure out for which values of z this will occur. I first tried rewriting the function as (1-e^(2i theta)) . But this seems to be getting me nowhere. Any thoughts?

Domianpv

Domianpv

Answered question

2022-09-30

Analyze the Complex Function by using the Principal log Branch
I am trying to analyze the function 1 z 2 , where the square root function is defined by the principal branch of the log function. I want to locate the the discontinuities.
I know the discontinuities will lie on the negative real axis but I cannot figure out for which values of z this will occur. I first tried rewriting the function as ( 1 e 2 i θ ). But this seems to be getting me nowhere. Any thoughts?

Answer & Explanation

Corbin Hanson

Corbin Hanson

Beginner2022-10-01Added 10 answers

Firstly we write
f ( z ) = 1 z 2 = e 1 2 ln ( 1 z 2 )
We have branch points for all z such that the argument of the log vanishes. We see that
1 z 2 = 0 z 1 , 2 = ± 1
We now need to investigate the point z = . In that manner we need to see if if there is a branch point az z = 0 for the function
g ( z ) = f ( 1 z ) = e 1 2 ln ( z 2 1 ) e 1 2 ln z 2
We can now conclude that the original function has two finite branch points, and one branch point at infinity. We chose a branch cut such that it connects 1 and and also 1 and . Note that this is actually one branch cut(in terms of the Riemann sphere)

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