KEK
Et ça? 
$$ \int_{a}^{b} f(x) dx = \lim_{n \to \infty} \sum_{k = 0}^{n} \left( \frac{b - a}{n} f \left(a + k \frac{b - a}{n}\right) \right)$$
$$ \int_{a}^{b} f(x) dx = \lim_{n \to \infty} \sum_{k = 0}^{n} \left( \frac{b - a}{n} f \left(a + k \frac{b - a}{n}\right) \right)$$
