\documentclass{article}

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\begin{document}

\[
P(X \in [\frac{k}{2^n},\frac{k+1}{2^n}]) \leq \frac{1}{n}\text{ Var}(X)
\]
\[
P\Big(X \in [\frac{k}{2^n},\frac{k+1}{2^n}]\Big) \leq \frac{\text{ Var}(X)}{n}
\]

\[
	x_n \to 0 \text{ quand } n \to \infty
\]

\[
	q(x,y) = \langle x,y \rangle
\]

\[
	[\widehat{f}(x)]^b_a = \widehat{f}(b) - \widehat{f}(a)
\]

\[
	x \in ]0,1]
\]

\[
	\pi = 3,141559
\]
\end{document}
