TeX джерело:

\begin{array}{l}\left\{ \begin{array}{l}{\log _4}(x + y) = 2,\\{\log _3}x + {\log _3}y = 2 + {\log _3}7;\end{array} \right.\;\left\{ \begin{array}{l}{\log _4}(x + y) = 2,\\{\log _3}(x \cdot y) = {\log _3}9 + {\log _3}7;\end{array} \right.\;\left\{ \begin{array}{l}x + y = 16,\\{\log _3}(xy) = {\log _3}63;\end{array} \right.\\\left\{ \begin{array}{l}x + y = 16,\\xy = 63;\end{array} \right.\;\left\{ \begin{array}{l}x = 16 - y,\\(16 - y) \cdot y = 63;\end{array} \right.\;\left\{ \begin{array}{l}x = 16 - y,\\16y - {y^2} - 63 = 0;\end{array} \right.\;\left\{ \begin{array}{l}x = 16 - y,\\{y^2} - 16y + 63 = 0;\end{array} \right.\\\left\{ \begin{array}{l}x = 16 - y,\\{y_1} = 7,{y_2} = 9.\end{array} \right.\end{array}