1. ## Continuity problem

Hello MHF, please help on this problem; (and by the way, we only did the continuity lesson )
We are given :
$f:[0,1]\rightarrow [0,1]$
$g:[0,1]\rightarrow [0,1]$
both $f$ and $g$ are continuious on $[0,1]$
$f(g(x)) = g(f(x))$
If $f(a) = a$ then $f(g(a)) = g(a)$

Show that $\exists \alpha \in [0,1] f(\alpha) = g(\alpha)$

P.S : use proof by contradiction

2. ## Re: Continuity problem

I tried to do this
let h(x) = f(x) - g(x)
for every x in [0,1] h(x)≠0
then for every x in [0,1] h(x) > 0 ( or < 0)
but after this i could't find a contradiction

3. ## Re: Continuity problem

Please I need to solve it before Monday morning.

4. ## Re: Continuity problem

Hi,
Since you need this by Monday morning, I can only assume it's either an exam question or homework for credit. So here are some hints:
Let a be a fixed point of f (f(a)=a) -- you need to prove why a exists. Now consider the sequence x1 = a and xn+1 = g(xn).

By the way, the above leads to a direct proof, not a proof by contradiction.

5. ## Re: Continuity problem

To start you off, suppose without loss of generality
$f(x)>g(x) \quad \text{ for an open interval in } [0,1]$
You'll get a contradiction along the way.

Note: Using the auxiliary function h you defined, could be used for a direct proof, but at that point you guys are assumed to know Intermediate Value Theorem, etc.

Disclaimer: If my line of thought is wrong or it has missing holes, please correct and/or inform me.

Hi again,