I'm struggling with the below problem.
For the following approximation:
$f''(x) \approx Af(x)+Bf(x+h)+Cf(x+2h)$
Find the coefficients A, B, C so that the degree of exactness is maximal and compute the error.
I have supposed that this is a Newton-Cotes quadrature, but I don't really know how should I compute the coefficients and the error.
Is the degree of exactness supposed to be the highest degree polynomial for which the formula is exact ? How is that value computed ?