The forward difference formula can be expressed as :
f'(x0) = (1/h)[f(x0+h)-f(x0)]-(h/2)f''(x0)-(h^2/6)f'''(x0)+O(h^3).
Use extrapolation to dervive an O(h^3) formula for f'(x0)
f'(x0) = (1/h)[f(x0+h)-f(x0)]-(h/2)f''(x0)-(h^2/6)f'''(x0)+O(h^3).
Use extrapolation to dervive an O(h^3) formula for f'(x0)