如 $\lim_{x \to 0} \frac{\sin x}{x}$ 渲染的是
$$
\begin{eqnarray}
\lim_{x \to 0} \frac{\sin x + x^2 + x^3}{x} & = & \lim_{x \to 0} \frac{\sin x }{x} + \lim_{x \to 0} \frac{x^2 }{x} + \lim_{x \to 0}\frac{x^3}{x}
\\ & = & \lim_{x \to 0}\frac{\sin x}{x}
\\ & = & 1
\end{eqnarray}
$$