Inequality Problem: Prove f^2 ≤ 1/4 (f')^2

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Homework Help Overview

The problem involves proving an inequality related to a function \( f \) that is continuously differentiable on the interval [0,1] with boundary conditions \( f(0) = f(1) = 0 \). The goal is to establish a relationship between the integral of the square of the function and the integral of the square of its derivative.

Discussion Character

  • Exploratory, Conceptual clarification, Assumption checking

Approaches and Questions Raised

  • The original poster attempts to understand how to derive the factor of \( \frac{1}{4} \) and how the boundary conditions influence the proof. They express uncertainty about progressing from their integral representations of \( f(x) \).

Discussion Status

Some participants suggest that the problem may relate to Wirtinger's Inequality, with one participant providing a link for further reading. This indicates a potential direction for exploration, although no consensus has been reached on the approach.

Contextual Notes

The discussion includes references to specific properties of the function \( f \) and its derivative, as well as the implications of the boundary conditions. There is an acknowledgment of the need for a deeper understanding of the inequality being discussed.

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Homework Statement


Let f\in C^{1} on [0,1], and f(0)=f(1)=0, prove that
\int_{0}^{1}(f(x))^{2}dx \leq \frac{1}{4} \int_{0}^{1} (f'(x))^{2}dx


Homework Equations





The Attempt at a Solution


what is the trick to produce a 1/4 there? and how to make use of f(0)=f(1)=0? well I know that f(0)=0 gives a formula like f(x)=\int_{0}^{x} f'(t)dt and f(1)=0 gives f(x)= -\int_{x}^{1} f'(t)dt. But seems that I cannot go further.
Any small hint would be great, thanks!
 
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anyone?...
 
Isn't this Wirtinger's Inequality?
 
yea, I'm reading it. cool. Thanks guys!
 

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