有理函数

多项式与多项式的比值

$$f(x) = \dfrac{P_m(x)}{Q_n(x)}$$

极限

极限值直接是函数值

$$\lim_{x \to x_0} f(x) = \lim_{x \to x_0} \dfrac{P_m(x)}{Q_n(x)} = \dfrac{P_m(x_0)}{Q_n(x_0)}$$