Real Polynomial Function is Continuous

Theorem
A polynomial function is continuous at every point.

Thus a polynomial function is continuous on every interval of $\R$.

Proof
From Linear Function is Continuous‎, setting $\alpha = 1$ and $\beta = 0$, we have that:
 * $\displaystyle \lim_{x \to c} \ x = c$

Repeated application of the Product Rule for Limits of Functions shows us that:
 * $\displaystyle \forall k \in \N: \lim_{x \to c} \ x^k = c^k$

Now let $P \left({x}\right) = a_n x^N + a_{n-1} x^{n-1} + \cdots + a_1 x + a_0$.

Now by repeated application of the Combined Sum Rule for Limits of Functions, we find that:
 * $\displaystyle \lim_{x \to c} \ P \left({x}\right) = P \left({c}\right)$

So whatever value we choose for $c$, we have that $P \left({x}\right)$ is continuous at $c$.

From the definition of continuity on an interval, the second assertion follows.