Uniform Convergence of Fn(x)=nx(1-x^2)^n on [0,1]?

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Homework Help Overview

The discussion revolves around the uniform convergence of the function \( F_n(x) = nx(1 - x^2)^n \) on the interval [0,1]. The original poster questions whether this function converges uniformly to 0 and expresses difficulty in demonstrating this using the formal definition of uniform convergence.

Discussion Character

  • Exploratory, Assumption checking, Mathematical reasoning

Approaches and Questions Raised

  • Participants explore the behavior of the function as \( n \) increases, particularly examining the supremum norm of \( F_n \). There are discussions about specific values of \( x \) and their implications for uniform convergence. Some participants question the assumptions regarding the limit function and the nature of convergence.

Discussion Status

The discussion is active, with participants providing hints and suggestions for further exploration. There is a recognition of the need to establish pointwise convergence before addressing uniform convergence. Multiple interpretations of the supremum norm and its implications for convergence are being examined.

Contextual Notes

Participants are considering the implications of the supremum norm and the behavior of the function at specific points as \( n \) varies. There is an emphasis on the need for clarity regarding the limit function and the conditions under which uniform convergence can be established.

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does Fn(x)= nx(1 - x^2)^n converge uniformly on [0,1]?
my first instinct was yes it converges uniformly to 0
but I can't seem to show that using the definition.

i get |nx(1 - x^2)^n|<=|nx|<=n for x in [0,1]

any tip or hint would be helpful
thanks
 
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What is the sup norm of f_n? That should give you the answer. Hint, it might help to remember basic analysis like turning points and points of infelxion...
 
for n large and x really small, namely x=1/n
i get that the sup{|f_n(x)|:x in [0,1]} = 1
so then it doesn't converge uniformly.
is that right?
 
That'll be right as long as you believe that the limit, if it were to exist, were the zero function, or something like it. After all, you need to have the notional idea of what it might converge to if it were to converge (and then to show that it is not uniform convergence). So, show it converges pointwise, and then show it is not uniform (if it were uniform then it would certainly be pointwise).

I don't agree that is important we say *for n really large* and *x really small* the the sup is something, rather than for ANY n the sup is..., after all the sup norm ought to be at least something independent of the n.
 
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