Obtain an upper bound on the absolute error when we compute $\displaystyle\int_0^6 \sin x^2 \,\mathrm dx$ by means of the composite trapezoid rule using 101 equally spaced points.
The formula I'm trying to use is:
$$ I = \frac{h}{2} \sum_{i=1}^n \Big[f(x_{i-1}) + f(x_i)\Big] - \frac{h^3}{12} \sum_{i=1}^n f^{''}(\xi_i) $$
But I'm lost on how to calculate the error and find a value for $\xi$. What's the general way of finding the error like this? Thanks for any help :)