Approximate Formula for Large x: Understand Derivation

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    Approximate Formula
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Discussion Overview

The discussion revolves around the derivation of an approximate formula for the arctangent function as x approaches infinity. Participants explore the mathematical reasoning behind the approximation and its relation to Taylor series and other functions.

Discussion Character

  • Exploratory, Technical explanation, Mathematical reasoning

Main Points Raised

  • One participant presents the approximation \(\arctan(x) \approx \pi/2 - 1/x + 1/3x^3...\) for large x and expresses confusion about its derivation.
  • Another participant suggests considering \(\arctan(1/x)\) as x approaches 0, noting the relationship \(\arctan(1/x) = \pi/2 - \arctan(x)\).
  • A third participant derives the derivative of the function \(f(x) = \arctan(1/x)\) and approximates it, arriving at \(f(x) \approx \pi/2 - x\), which they find satisfactory.
  • A later reply indicates that the participant was able to derive additional terms in the approximation, expressing gratitude for the assistance.

Areas of Agreement / Disagreement

The discussion does not reach a consensus on the derivation method, as participants explore different approaches and insights without resolving the initial confusion.

Contextual Notes

Participants rely on different mathematical perspectives, including Taylor series and derivatives, but the assumptions and steps leading to the approximation remain partially unresolved.

Yegor
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There exist such a formula for large x:
[tex]\arctan(x)\approx \pi/2-1/x+1/3x^3...[/tex]
I can't understand how it is derived. I tried to get it from Taylor series (for x -> infinity) and understood that here is something different. Can someone help me?
Thank you
 
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have you tried arctan(1/x) for x->0?

and note:
arctan(1/x) = Pi/2 - arctan(x)
 
Last edited:
Hm. This is what i got:
[tex]f(x)=\arctan(1/x); <br /> f'(x)=-\frac{1}{1+x^2}; <br /> f(x)\approx f(0)+f'(0)(x-0)=\pi/2-x[/tex]
yes. it looks good
 
Great. i got next terms too. Thank you very much.
 

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