Hi, 1. The problem statement, all variables and given/known data Interpolation for the function f(x)=cos(x) for evenly distributed values of x in [0,π] (h=xi+1-xi, xi=ih, i=0,1,...,πh) is carried out. Also known are f(xi). I am asked to determine the value of h so that the interpolation's error is ≤ 5*10-8. 2. Relevant equations 3. The attempt at a solution I have found f'''(x) for x in [0,π] to be ≤ 1. Now I am stuck with evaluating |(x-xi+1)(x-xi)(x-xi-1)|. I'd truly appreciate some assistance. Thanks in advance!