What Is the Fourth Derivative Test and How Does It Determine Extrema?

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Discussion Overview

The discussion revolves around the concept of the fourth derivative test in calculus, particularly in relation to determining extrema of functions. Participants explore its definition, application, and implications, while also questioning its existence and relevance in certain cases.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant presents a remark and an example regarding the fourth derivative test, suggesting that if the second derivative at a point is zero, one can apply the fourth derivative test to determine if that point is a minimum or maximum.
  • Another participant expresses uncertainty about the existence of a fourth derivative test, indicating a lack of recollection regarding its formal definition.
  • A third participant suggests that the application described may actually be a misinterpretation of the second derivative test, implying that the fourth derivative test is not a standard concept.
  • A fourth participant outlines a general approach to determining extrema by continuing to take derivatives until a non-zero derivative is found, noting that the parity of the derivative affects the classification of the point.

Areas of Agreement / Disagreement

Participants do not appear to reach a consensus on the existence or validity of the fourth derivative test, with multiple competing views and interpretations presented throughout the discussion.

Contextual Notes

Some assumptions regarding the application of derivative tests remain unaddressed, such as the conditions under which these tests are applicable and the definitions of terms used in the discussion.

KLscilevothma
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I was given a remark and an example in my notes.

Remark: If f ''(xo)=0, then fourth derivative test

Example:
f(x)=x4
f ''(0)=0
apply the fourth derivative test
f(4)(x)=24 >0
therefore (0,0) is a minimun point

What exacly is the fourth derivative test? I can't find any resources from the internet. What if the function f(x)=x^5 ? Do we have the eighth derivative test?
 
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I don't recall there being a 4th derivative test.
 
It looks as if you're applying the second derivative test to a second derivative.
 
The general idea (when the first derivative is 0) is to keep taking derivatives until you get one that's not 0. If it is an odd derivative, then you've got a horizontal inflection point. If it is an even derivative, then the sign distinguishes between max (-) and min (+).
 

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