$a^2 + b^2 = c^2$

\(1+2+\dots+n=\frac{n(n+1)}{2}\)  

$$ \frac{d}{dx}\left( \int_{0}^{x} f(u)\,du\right)=f(x) $$

\begin{align*}
e^x & = 1 + x + \frac{x^2}{2} + \frac{x^3}{6} + \cdots \\
    & = \sum_{n\geq 0} \frac{x^n}{n!}
\end{align*}