Math

$$\begin{vmatrix}a & b\\
c & d
\end{vmatrix}=ad-bc$$

$$\begin{vmatrix}a & b\ c & d \end{vmatrix}=ad-bc$$

You can also do inline math like $e^{2i\pi} = 1$ .

Obsidian uses Mathjax. You can check which packages are supported in Mathjax here.