$x^2+y^2$

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

\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*}

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