> Here is a formula:

$$
\dfrac{\partial}{\partial t}(
	\dfrac{\partial \mathcal{L}}{\partial \dot{q}_k}
) - \dfrac{\partial \mathcal{L}}{\partial q_k} = 0
$$

> And here is a circuit:

```tikz
\usepackage{circuitikz}

\begin{document}
	\begin{circuitikz} \draw
		(0,0) to[battery] (0,4)
  		to[ammeter] (4,4) -- (4,0)
  		to[lamp] (0,0)
		;
	\end{circuitikz}
\end{document}
```

