How Can We Prove the Global Minimum of the Absolute Value Function at x=0?

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Discussion Overview

The discussion centers on proving the global minimum of the absolute value function, specifically at the point x=0. Participants explore various approaches to establish that there is no point c in the real numbers such that f(c) is less than f(0), considering the function's properties and limitations.

Discussion Character

  • Technical explanation
  • Mathematical reasoning

Main Points Raised

  • One participant asserts that the absolute value function f(x)=|x| has a global minimum at x=0 and seeks a rigorous proof for this claim.
  • Another participant suggests that the proof could be based on the definition of the absolute value being non-negative, implying that no point c can exist where f(c) is less than f(0).
  • A third participant provides a breakdown of the function's behavior, stating that for x>0, f(x) is positive; for x=0, f(x) equals zero; and for x<0, f(x) is also positive, which supports the claim of a minimum at x=0.
  • Another participant proposes using derivatives for the analytic portions of the function, indicating a need to consider the function's piecewise nature.

Areas of Agreement / Disagreement

Participants present multiple viewpoints on how to approach the proof, with no consensus on a single method or resolution of the discussion.

Contextual Notes

Participants note the non-differentiability of the function at x=0, which affects the applicability of certain theorems, such as Fermat's critical point theorem.

Bipolarity
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The absolute value function f(x)=|x| has a global minimum at x=0. How could we prove this rigorously? In other words, how could we prove that there is no point c \ \epsilon \ ℝ such that f(c)&lt;f(0)

(Obviously, the function is not differentiable at x=0 so we cannot apply Fermat's critical point theorem).

BiP
 
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I think the rigorous proof just goes something like "by definition, the absolute value of a real number is non-negative, therefore no such c exists."
 
  1. If ##x>0## then ##f(x) = x## so ##f(x) > 0##,
  2. If ##x=0## then ##f(x) = x = 0##,
  3. If ##x < 0## then ##f(x) = -x## and so ##f(x) > 0##,
and that's it.
 
You can also use the derivatives for each analytic portion of the function (you have to break it up into two analytic functions each with their own domain).
 

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