§3. Функции и их свойства — 7. Свойства чётности и нечётности функций — 109 — стр. 37

\(\left\{\begin{array}{l}y = 0.4x + 3 \\y = 5 - 0.6x\end{array}\right. \Leftrightarrow \left\{\begin{array}{c}0.4x + 3 = 5 - 0.6x \\y = 0.4x + 3\end{array}\right. \Leftrightarrow \left\{\begin{array}{c}0.4x + 0.6x = 5 - 3 \\y = 0.4x + 3\end{array}\right. \Leftrightarrow\\ \Leftrightarrow \left\{\begin{array}{c}x = 2 \\y = 0.4 \cdot 2 + 3 = 3.8\end{array}\right. \Leftrightarrow \{x=2, \, y=3.8\}\)

Точка пересечения \((2 ; 3.8)\).

\(\begin{array}{c}\left\{\begin{array}{c}y = \frac{1}{3}x + 11 \\y = -\frac{2}{9}x + 4\end{array}\right. \Leftrightarrow \left\{\begin{array}{c}\frac{1}{3}x + 11 = -\frac{2}{9}x + 4 \\y = -\frac{2}{9}x + 4\end{array}\right. \Leftrightarrow \left\{\begin{array}{c}\frac{1}{3}x + \frac{2}{9}x = 4 - 11 \\y = -\frac{2}{9}x + 4\end{array}\right. \Leftrightarrow\\\Leftrightarrow \left\{\begin{array}{c}\frac{5}{9}x = -7 \\y = -\frac{2}{9}x + 4\end{array}\right. \Leftrightarrow \\ \Leftrightarrow \left\{\begin{array}{c}x = -7 \cdot \frac{9}{5} = -\frac{63}{5} = -\frac{126}{10} = -12.6 \\y = -\frac{2}{9} \cdot \left(-\frac{63}{5}\right) + 4 = \frac{14}{5} + 4 = 2.8 + 4 = 6.8\end{array}\right.\end{array}\)

Точка пересечения \((-12.6 ; 6.8)\).