The trapezoid rule
$$\int_a^b f(x)~dx = \sum\limits_{i=1}^{n1} \frac{f(x_{i+1})+f(x_i)}{2}\Delta x_i $$

This example was developed in Excel 2013 Pro 64 bit.

Revised:
$$\int_a^b f(x)~dx = \sum\limits_{i=1}^{n1} \frac{f(x_{i+1})+f(x_i)}{2}\Delta x_i $$