TeX джерело:
\left\{ \begin{array}{l}a - b = 2,\\a + b = 16;\end{array} \right.\quad \left\{ \begin{array}{l}2a = 18,\\ - 2b = - 14;\end{array} \right.\quad \left\{ \begin{array}{l}a = 9,\\b = 7.\end{array} \right.