\documentclass{article}

\begin{document}

\section{Sample LaTeX Document with Math Symbols}

Here are some math symbols and commands:

1. Infinity: $\infty$
2. Element of: $a \in A$
3. Angle: $\angle ABC$
4. Approximation: $a \approx b$
5. Union: $A \cup B$
6. Intersection: $A \cap B$
7. Big union: $\bigcup_{i=1}^{n} A_i$
8. Big intersection: $\bigcap_{i=1}^{n} A_i$
9. Down arrow: $\downarrow$
10. Double down arrow: $\Downarrow$
11. Copyright symbol: $\copyright$
12. Quadruple space: $a \qquad b$
13. Empty set: $\emptyset$
14. Aleph symbol: $\aleph$
15. Product: $\prod_{i=1}^{n} a_i$
16. Integration: $\int f(x) \, dx$
17. Clubsuit: $\clubsuit$
18. dot: $\dot{B}$

\end{document}

