三角形
求三角形面积
已知底和高
S=1/2×底×高
$$ \sum_{i=1}^{n} i = \frac{n(n+1)}{2} $$
\[
E = mc^2
\]$$
\begin{aligned}
a & =b+c \\
& =d+e
\end{aligned}
$$
S=1/2×底×高
$$ \sum_{i=1}^{n} i = \frac{n(n+1)}{2} $$
\[
E = mc^2
\]$$
\begin{aligned}
a & =b+c \\
& =d+e
\end{aligned}
$$