Compute forward and backward difference approximations of O(h) and O(h2), and central difference approximations of O(h2) and

Question:

Compute forward and backward difference approximations of O(h) and O(h2), and central difference approximations of O(h2) and O(h4) for the first derivative of y = cos x at x = π/4 using a value of h = π/12. Estimate the true percent relative error εt for each approximation.