多项式与多项式的比值
f(x)=Pm(x)Qn(x) f(x) = \dfrac{P_m(x)}{Q_n(x)} f(x)=Qn(x)Pm(x)
极限值直接是函数值
limx→x0f(x)=limx→x0Pm(x)Qn(x)=Pm(x0)Qn(x0) \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)} x→x0limf(x)=x→x0limQn(x)Pm(x)=Qn(x0)Pm(x0)