$$
\begin{align}
sum&=(a+1)(b+1)\\
&=(a+1)(mid-a+1)\\
&=a\cdot mid-a^2+a+mid-a+1\\
&=-a^2+a\cdot mid+1+mid\\
&=-(a^2-a\cdot mid)+1+mid\\
&=-(a^2-a\cdot mid+\frac{mid^2}{4})+1+mid+\frac{mid^2}{4}\\
&=-(a-\frac{mid}{2})^2+1+mid+\frac{mid^2}{4}
\end{align}
$$
\begin{aligned}
sum&=(a+1)(b+1)\\
&=(a+1)(mid-a+1)\\
&=a\cdot mid-a^2+a+mid-a+1\\
&=-a^2+a\cdot mid+1+mid\\
&=-(a^2-a\cdot mid)+1+mid\\
&=-(a^2-a\cdot mid+\frac{mid^2}{4})+1+mid+\frac{mid^2}{4}\\
&=-(a-\frac{mid}{2})^2+1+mid+\frac{mid^2}{4}
\end{aligned}
这两个在 Typora 上是等价的,但是到了洛谷就只有第二个可以正常显示.
sum=(a+1)(b+1)=(a+1)(mid−a+1)=a⋅mid−a2+a+mid−a+1=−a2+a⋅mid+1+mid=−(a2−a⋅mid)+1+mid=−(a2−a⋅mid+4mid2)+1+mid+4mid2=−(a−2mid)2+1+mid+4mid2
希望可以增强洛谷博客的适应能力(或许是洛谷用 KaTeX 渲染的缘故?)