Simple numerical differentiation - Euler method
Forward difference
\(\frac{f(x + h) - f(x)}{h}\) with small h (but larger than machine epsilon)
Central difference
\(\frac{f(x + h) - f(x - h)}{2h}\) with small h
\(\frac{f(x) - f(x - h)}{h}\) is not used. Explain why.