Show that arctan(x) exists and is continuous

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Homework Help Overview

The problem involves demonstrating the existence and continuity of the inverse function arctan(x) based on the properties of the tangent function over the interval (-π/2, π/2). The original poster attempts to establish that tan(x) is bijective and continuous, leading to the conclusion that arctan(x) exists.

Discussion Character

  • Exploratory, Conceptual clarification, Assumption checking

Approaches and Questions Raised

  • Participants discuss the implications of the continuity of tan(x) and its inverse, with suggestions to explore contradictions arising from the assumption of discontinuity in arctan(x). There is also a mention of the relationship between continuous functions and their inverses.

Discussion Status

The discussion is ongoing, with participants offering suggestions and questioning the assumptions related to continuity. There is no explicit consensus yet, but some guidance has been provided regarding potential approaches to the problem.

Contextual Notes

Participants are considering the properties of continuity and the behavior of functions over specified intervals, with an emphasis on the relationship between open sets and continuity.

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Homework Statement



Show tan(x): (-pi/2, pi/2) -> R has a continuous inverse arctan(x) : R -> (-pi/2, pi/2).

You may assume that tan(x) is continuous and strictly increasing on the given domain, and tends to +/- \infty at +/- pi/2

Homework Equations





The Attempt at a Solution



I think I have shown that tan(x) has an inverse on this domain by showing it is bijective.

However, I am unsure how to go about showing that arctan(x) is continuous.
 
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You could try considering tan(arctan(x))=x and show that if arctan(x) is not continuous, it leads to a contradiction.

(I'm just offering a suggestion. I think it'll work, but I didn't actually try it.)
 
Continuous functions can have discontinuous inverses.

I'm not sure if this is possible when the domain and codomain are intervals, though. I suspect not.
 
What characterizations of continuity have you learnt? Try showing that tan takes every open set to an open set.
 

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