The identity of symmetry is: $$$\begin{pmatrix} m \\ n \end{pmatrix}=\begin{pmatrix} m \\ m-n \end{pmatrix}$$$
For example:
$$\begin{pmatrix} 5 \\ 2\end{pmatrix}=\begin{pmatrix} 5 \\ 5-2\end{pmatrix} = \begin{pmatrix} 5 \\ 3\end{pmatrix} $$
$$\begin{pmatrix} 7 \\ 2\end{pmatrix} = \begin{pmatrix} 7 \\ 5\end{pmatrix} $$
$$\begin{pmatrix} 100 \\ 99\end{pmatrix} = \begin{pmatrix} 100 \\ 1\end{pmatrix}=100 $$