# Thread: Sequence of function.

1. ## Sequence of function.

Let $(f_n)^\infty_{n=1}$ be a sequence of functions which are defined on $[a,b]$, and uniformly converges there to bounded function $f$. Let $\Phi\in C(\mathbb{R})$ which is continuous function on all $\mathbb{R}$.
Prove that the sequence $(\Phi(f_n))^\infty_{n=1}$ uniformly converges and find the limit function.

Thank you!

2. Originally Posted by Also sprach Zarathustra
Let $(f_n)^\infty_{n=1}$ be a sequence of functions which are defined on $[a,b]$, and uniformly converges there to bounded function $f$. Let $\Phi\in C(\mathbb{R})$ which is continuous function on all $\mathbb{R}$.
Prove that the sequence $(\Phi(f_n))^\infty_{n=1}$ uniformly converges and find the limit function.

Thank you!
What have you tried? Are you going to just use the definition? If so, maybe seeing what $\lim\text{ }\Phi(f_n)$ is equal to would help. First, just as a matter of formality we really are considering $\Psi=\Phi\mid_X$ where $X=\bigcup_{n\in\mathbb{N}}f_n\left([a,b]\right)$ and the restriction of a continuous function is continuous. So, let $\varphi(x)=\lim\text{ }\Psi\left(f_n(x)\right)$. Then, for a fixed $x_0\in [a,b]$ we have that $\varphi(x_0)=\lim\text{ }\Psi\left(f_n(x_0)\right)\overset{{\color{red}*}} {=}\Psi\left(\lim\text{ }f_n(x_0)\right)=\Psi\left(f(x_0)\right)$ so that we see $\varphi(x)=\lim\text{ }\Psi\left(f_n(x)\right)=\Psi\left(f(x)\right)$. Now, tell me, what did I use at $\color{red}*$?