Approximate Formula for Large x: Understand Derivation

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SUMMARY

The forum discussion focuses on the derivation of the approximate formula for large values of x in the context of the arctangent function, specifically: \(\arctan(x) \approx \frac{\pi}{2} - \frac{1}{x} + \frac{1}{3x^3}...\). Users explored the relationship between \(\arctan(1/x)\) and \(\arctan(x)\), leading to the conclusion that as x approaches infinity, the Taylor series expansion is not applicable, and an alternative approach is necessary. The discussion highlights the derivation of the first few terms of the approximation, confirming the validity of the formula.

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  • Understanding of the arctangent function and its properties
  • Familiarity with Taylor series expansions
  • Basic calculus concepts, including derivatives
  • Knowledge of limits and asymptotic behavior
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  • Investigate the relationship between \(\arctan(x)\) and \(\arctan(1/x)\)
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Mathematicians, calculus students, and anyone interested in advanced mathematical analysis of functions, particularly those studying asymptotic behavior and series expansions.

Yegor
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There exist such a formula for large x:
\arctan(x)\approx \pi/2-1/x+1/3x^3...
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:
f(x)=\arctan(1/x); <br /> f&#039;(x)=-\frac{1}{1+x^2}; <br /> f(x)\approx f(0)+f&#039;(0)(x-0)=\pi/2-x
yes. it looks good
 
Great. i got next terms too. Thank you very much.
 

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