Is the Derivative of Arctangent Equal to 1/x?

  • Context: Undergrad 
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Discussion Overview

The discussion revolves around the derivative of the arctangent function, specifically whether it can be expressed as both \(\frac{1}{1+x^2}\) and \(\frac{\arctan x}{x}\). Participants explore the implications of these expressions and the context in which they arise.

Discussion Character

  • Debate/contested, Technical explanation

Main Points Raised

  • Some participants reference Wolfram|Alpha, which provides two different expressions for the derivative of arctangent: \(\frac{1}{1+x^2}\) and \(\frac{\arctan x}{x}\).
  • One participant clarifies that the second expression involves a notation \(\frac{d}{d \times x}\), suggesting it simplifies to \(\frac{1}{x}\).
  • Another participant expresses confusion about the meaning of the notation \(\frac{d}{d \times x}\).
  • There is a mention of the importance of the input given to Wolfram|Alpha, indicating that different inputs may yield different interpretations or results.

Areas of Agreement / Disagreement

Participants do not reach a consensus on whether both expressions for the derivative are valid or under what conditions they apply. The discussion remains unresolved regarding the equivalence of the two forms.

Contextual Notes

There are unresolved questions about the notation used and the assumptions behind the expressions provided by Wolfram|Alpha. The discussion highlights potential differences in interpretation based on input.

dimension10
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According to Wolfram|Alpha, sometimes, the derivative of arctangent is

[tex]\frac{d}{dx}\arctan x =\frac{1}{1+{x}^{2}}[/tex]

and sometimes,

[tex]\frac{d}{dx}\arctan x =\frac{\arctan x}{x}[/tex]

So are both of them equal?
 

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The second case is actually
[tex]\frac{d}{d\times x}\arctan (x)=\frac{\arctan (x)}{x}[/tex].
:smile:
 
Okay, you have lost me. What does
[tex]\frac{d}{d\times x}[/tex]
mean?
 
d over d multiplied by x, where d is a constant. Wolframalpha simplifies this to 1/x.
 
Oh. So that must have happened the other time too...
 
Compare:
attachment.php?attachmentid=37860&stc=1&d=1312884751.jpg

Notice the blank between d and x in the left one.
What input did you give in each time?
 

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asmani said:
d over d multiplied by x, where d is a constant. Wolframalpha simplifies this to 1/x.
Thanks.
 

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