Does the Arzela-Ascoli Theorem Ensure a Converging Subsequence for {F_n}?

[e(ho0n3]

Homework Statement
Let \{f_n\} be a uniformly bounded sequence of functions which are Riemann-integrable on [a,b]. Let
F_n(x) = \int_a^x f_n(t) \, dt
Prove that there exists a subsequence of \{F_n\} which converges uniformly on [a,b].

The attempt at a solution
I was thinking, since \{f_n\} is uniformly bounded, there is an M such that F_n(x) \le M(x - a) \le M(b - a) for all n, for all x. Now this automatically means that \{F_n\} converges uniformly right? But then if \{F_n\} converges uniformly, why is the problem requesting for a subsequence? I must have done something wrong.

 

[Dick]

The f_n aren't given to be convergent. Sure the F_n are bounded, but that certainly doesn't mean they are convergent. Can't you think of a theorem that guarantees the existence of a uniformly convergent subsequence in a family of functions? What are it's premises?

 

[e(ho0n3]

You mean the Arzela-Ascoli Theorem right? The Wikipedia article actually states what I'm trying to prove I think:

For example, the theorem's hypotheses are satisfied by a uniformly bounded sequence of differentiable functions with uniformly bounded derivatives.

the hypotheses being that the sequence must be uniformly bounded and equicontinuous. I have already shown that the sequence is uniformly bounded right? So all I need to show is that it is equicontinuous. I think I can handle that.

 

[Dick]

You mean the Arzela-Ascoli Theorem right? The Wikipedia article actually states what I'm trying to prove I think:



the hypotheses being that the sequence must be uniformly bounded and equicontinuous. I have already shown that the sequence is uniformly bounded right? So all I need to show is that it is equicontinuous. I think I can handle that.

You've got it.