What are the solutions of w=tan z if w doesn't equal +i or -i?

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Discussion Overview

The discussion centers on the solutions of the equation w = tan z, specifically exploring the conditions under which w does not equal +i or -i. Participants are examining the implications of this condition in the context of complex analysis, without resorting to the arctan w identity.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant seeks to demonstrate that any w not equal to +i or -i is the image of some z in C, noting that while they can show that tan z cannot equal +i or -i, this does not directly address the original question.
  • Another participant points out that tan is expressed as sin over cos, suggesting a relationship to exponentials in z, but does not elaborate on how this aids the original inquiry.
  • There is a reiteration that if w equals +i or -i, the expression becomes undefined, which is acknowledged but not seen as a resolution to the problem.
  • A participant mentions that they are not permitted to use the formula for arctan w, indicating a constraint on the methods available for solving the problem.
  • One participant proposes that tan z can be viewed as e^z, translated such that i and -i correspond to 0 and infinity, and suggests the potential application of Picard's theorem.
  • Another participant emphasizes that deriving the inverse function is distinct from using it, asserting that there is no solution in terms of the exponential representation of the functions.
  • A final contribution presents a fact about the unit disc being the universal covering space of the sphere minus three points, concluding that since tan(z) is not constant, it cannot miss more than the two points i and -i.

Areas of Agreement / Disagreement

Participants express differing views on the implications of the conditions set for w, with no consensus reached on the solutions or methods to approach the problem. The discussion remains unresolved regarding the specific solutions of w = tan z under the given constraints.

Contextual Notes

Participants note limitations in their approaches, including the restriction against using the arctan w identity and the need to derive rather than use certain functions. The discussion also reflects a dependence on the definitions of holomorphic maps and covering spaces.

Mark C
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Hi

If w=tan z

How would I show that any w not equal to +i or -i,
is the image of some z in C, and what are the solutions
of w=tan z if w doesn't equal to +i or -i?
I can easily show that tan z can never equal +i or -i,
but that's not the same thing also.

Note: without using the arctan w identity.

Thank you
 
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tan is sin over cos, right? and these are simply exponentials in z, too. does that help?
 
Well, yes I know that, I can show that if w=i or -i then the expression is not defined, but that's not the same thing.

thank you anyway
 
Mark C said:
Well, yes I know that, I can show that if w=i or -i then the expression is not defined, but that's not the same thing.

thank you anyway
Have you derived the inverse function using the exponentials ?
 
I am not supposed to use the formula for arctan w.
 
tanz is the same as e^z but translated so that i , -i correspond to 0 and infinity. maybe. or you could use picards theorem.
 
Last edited:
Deriving it isnt' the same as "using it" you simply show that there is no solution in terms of the exponential version of the functions.
 
here is a quick argument for you.
fact: the unit disc is the universal covering space of: "the sphere minus 3 points".

corollary: if a holomorphic map to the sphere misses three points, then it factors through the unit disc, hence is constant, by liouville's theorem.

since tan(z) is not constant it cannot miss any more than the two points i and -i.
 

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