minor edit.

integration.tex

-\subsection{Numerical integration}
+\subsection{Newton–Cotes formulas}
 We derived the following formulas for evaluating the following integral numerically: $I = \int_{x_1}^{x_2} f(x) \, dx.$
 \begin{eqnarray}
 \mathit{Midpoint~rule:} & I = h \, f(\frac{x_1+x_2}{2})  + \mathcal{O}\,(h^3) \\