The formula used to compute an approximation for the second derivative of a function $f$ at a point $X_0$ is

$\frac{f(x_0 +h) + f(x_0 – h)}{2}$

$\frac{f(x_0 +h)  f(x_0 – h)}{2h}$

$\frac{f(x_0 +h) + 2f(x_0) + f(x_0 – h)}{h^2}$

$\frac{f(x_0 +h)  2f(x_0) + f(x_0 – h)}{h^2}$