[latexpage] At first, we sample $f(x)$ in the $N$ ($N$ is odd) equidistant points around $x^*$: \[ f_k = f(x_k),\: x_k = x^*+kh,\: k=-\frac{N-1}{2},\dots,\frac{N-1}{2} \] where $h$ is some step. Then we interpolate points $\{(x_k,f_k)\}$ by polynomial \begin{equation} \label{eq:poly} P_{N-1}(x)=\sum_{j=0}^{N-1}{a_jx^j} \end{equation} Its coefficients $\{a_j\}$ are found as a solution of system of linear equations: \begin{equation} \label{eq:sys} \left\{ P_{N-1}(x_k) = f_k\right\},\quad k=-\frac{N-1}{2},\dots,\frac{N-1}{2} \end{equation} \[ f(x)=\int_1^{\infty}\frac{1}{x^2}\,\mathrm{d}x=1 \] \[ E = mc^2 \] \[ \frac{d}{dx} \left( x^2 \right) = 2x \] \[ \alpha, \beta, \gamma, \delta \] \[ \lim_{x \to \infty} \frac{1}{x} = 0 \] \[ \alpha, \beta, \gamma, \delta \] \[ \binom{n}{k} \]