Solution (source code)

= Solution

\b[True.] For each $n$, the <Weierstrass approximation theorem> gives a polynomial $P_n$ such that
$$
\sup_{|x|\leq n}|P_n(x)-f(x)|<\frac1n.
$$
For each fixed $x\in\mathbb R$, this estimate applies once $n\geq|x|$, so $P_n(x)\to f(x)$ pointwise.