Show that arctan(x) exists and is continuous

  • Thread starter Kate2010
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In summary, tan(x): (-pi/2, pi/2) -> R has a continuous inverse arctan(x) : R -> (-pi/2, pi/2), with the assumption that tan(x) is continuous and strictly increasing on the given domain and tends to +/- \infty at +/- pi/2. To show that arctan(x) is continuous, one can use the fact that tan(arctan(x))=x and consider the possibility of a discontinuous inverse leading to a contradiction. It is also worth noting that continuous functions can have discontinuous inverses, but this may not be possible when the domain and codomain are intervals. One can also try showing that tan takes every open set to an
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Kate2010
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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 +/- [tex]\infty[/tex] 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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  • #2
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.)
 
  • #3
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.
 
  • #4
What characterizations of continuity have you learnt? Try showing that tan takes every open set to an open set.
 

1. What is arctan(x)?

Arctan(x) is the inverse function of tangent, denoted as tan^-1(x). It is also known as the arc tangent function and is used to find the angle whose tangent is x.

2. How do you show that arctan(x) exists?

To show that arctan(x) exists, we need to prove that the inverse function of tangent exists for all real numbers. This can be done by showing that the tangent function is one-to-one and onto, meaning it has a unique output for every input and that every real number has a corresponding input in the tangent function.

3. What is the domain and range of arctan(x)?

The domain of arctan(x) is all real numbers, while the range is limited between -π/2 and π/2, or -90 degrees and 90 degrees, respectively.

4. How is the continuity of arctan(x) demonstrated?

The continuity of arctan(x) can be demonstrated by showing that it is differentiable for all real numbers. This can be done by proving that the tangent function, which is the derivative of arctan(x), is continuous for all real numbers.

5. Why is it important to show that arctan(x) exists and is continuous?

It is important to show that arctan(x) exists and is continuous because it allows us to use this function in various mathematical calculations and applications. It is also a fundamental concept in trigonometry and calculus.

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