Given two real polynomials $$\begin{array}{rcl}p(x)&=&a_nx^n + \ldots + a_1x + b_0,\\p(x)&=&b_mx^m + \ldots + b_1x + b_0,\end{array}$$ with the degrees $n$ an $m$, let $D:=\{x\in\mathbb R:~q(x)\neq 0\}$. A rational function is a function defined by
\[r:=\begin{cases} \mathbb D&\to\mathbb R\\ x&\to r(x):=\frac{p(x)}{q(x)}. \end{cases}\]
