设函数$y = f(x)$在点$x = x_0$处可导，且$x = x_0$为极值点，则$f'(x_0) =$（　　）.

求极限$\lim\limits_{x \to +\infty} \dfrac{\ln x}{e^{-x} - e^x}$.

函数$y = 2x + 1$的反函数为$y =$（　　）.