LaTeX

&：对齐

\\：换行

\begin{align*}

\end(align*)：固定框架

\begin{align*}
\lim_{x \to 3} \frac{x^2 - 6x + 9}{x^2 - 5x + 6} &= \lim_{x \to 3} \frac{(x - 3)^2}{(x - 2)(x - 3)} \\
&= \lim_{x \to 3} \frac{x - 3}{x - 2} \\
&= \frac{3 - 3}{3 - 2} \\
&= 0
\end{align*}

\begin{align*}
x^2 - 2xy + 9 &= 0 \\
(x^2)' - (2xy)' + (9)' &= 0 \\
2x - 2\left(y + xy'\right) &= 0 \\
2x - 2y - 2xy' &= 0 \\
2xy' &= 2x - 2y \\
y' &= \frac{2x - 2y}{2x} \\
y' &= \frac{x - y}{x}
\end{align*}