\begin{matrix} \int_{a}^{b} f (x) d x = = lim n \to \infty \frac{1}{n} (f (a + \frac{b - a}{n}) + f (a + 2 \frac{b - 2}{n}) + \dots + f (b)) \end{matrix}

${\begin {array} {l} \int_a^b f(x)\,dx = \\ = \lim\limits_{n \rightarrow \infty} \frac {1} {n} \bigg ( f \left (a + \frac {b - a} {n} \right) + f \left (a + 2 \frac {b - 2} {n} \right) + \ldots + f(b) \bigg) \end {array}}$