Mean and weighted mean comparison

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Discussion Overview

The discussion revolves around the comparison between the weighted mean and the arithmetic mean, specifically exploring the inequality (c-b)f(a)+(b-a)f(c)>(c-a)f(b) under the condition that f is continuous and strictly increasing on the interval [a,c], where a

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • One participant questions the truth of the proposed inequality and suggests testing it with simple example functions.
  • Another participant confirms the inequality holds for the function f(x) = x² over positive real domains.
  • A different participant prompts checking the inequality with the identity function f(x) = x and comparing it to linear interpolation.
  • Further, a participant proposes testing the inequality with the function f(x) = √x, using specific values for a, b, and c.
  • One participant acknowledges a mistake and modifies the question, suggesting that if f'(x) is strictly increasing, the conjecture appears to hold, but emphasizes the need for a general proof.
  • Another participant introduces the mean value theorem, suggesting that if the inequality fails, it could indicate the existence of points x and y where the derivative relationship does not hold.
  • Finally, a participant claims to have solved the problem by analyzing the slopes of the function at specific points, concluding that the inequality holds under the given conditions.

Areas of Agreement / Disagreement

Participants express differing views on the validity of the inequality, with some supporting its truth under specific conditions while others remain skeptical and seek further proof. The discussion does not reach a consensus on a general proof.

Contextual Notes

Participants rely on specific functions and conditions to test the inequality, but the generality of the proof remains unresolved. The discussion highlights dependencies on the properties of the function f and the assumptions made regarding its derivatives.

gianeshwar
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Dear Friends!
Is weighted mean greater than mean?
Actually i need to prove (c-b)f(a)+(b-a)f(c)>(c-a)f(b) when when f is continuous and strictly increasing in [a,c],where a<b<c.
 
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Is what you are trying to prove even true? Can you check against some simple example functions?
 
Dear friend!Thank You for response!
I have checked it and it comes true for f(x) equal to x square for the positive real domains.
 
Have you checked against the identify function, f(x) = x?

And have you compared the formula in question to linear interpolation?
 
gianeshwar said:
I have checked it and it comes true for f(x) equal to x square for the positive real domains.

Try f(x) = \sqrt{x},\ a = 0,\ b = 1,\ c = 9
 
Thank You dear friends!
I had realized my mistake and an modifying the question.
Now ingnore first part of question and assume that if in addition it is specified that f'(x) is strictly increasing then the cnjecture seems true.BUT I NEED GENERAL PROOF.
 
The mean value theorem should have something to contribute. Consider the slopes of the lines from (a,f(a)) to (b,f(b)), from (b,f(b)) to (c,f(c)) and from (a,f(a)) to (c,f(c)).

If the inequality fails to hold then you should be able to demonstrate the existence of two points x and y such that x > y and f'(x) <= f'(y)
 
Thank You all friends!
Ultimately could solve as follows:
f(b)-f(a)/b-a less than f(c)-f(b)/c-b,because f'(p) less than f'(q) due to f'(x) strictly increasing and p in (a,b) and q in (b,c).
 

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