# Limitation

> 一旦数学入门后，除了式子，什么都不想看\(感觉最高效\)。（但是，对于没入门的小朋友，还是需要大量的详细的算法或思路的步骤讲解）
>
> Once you know coding very well, you don't want to see other stuff, you'll be focus on codes, you'll think that was the greatest way to learn new things. \(But to those who is new to this field, books or tutorials with fully explanation is important\)

$$
\begin{align*}
& \lim_{(x, y) \to (0, 2)} \frac{\sin(xy)}{x}
\\ \\
=& \lim_{(x, y) \to (0, 2)} [\frac{\sin(xy)}{xy} \cdot y]
\\ \\
=& \lim_{xy \to 0} \frac{\sin(xy)}{xy} \cdot \lim_{y \to 2} y
\\ \\
=& 1 \cdot 2
\\ \\
&\text{ # approaching but not equal}
\end{align*}
$$

