\[\boxed{\text{1118.\ }\text{еуроки}\text{-}\text{ответы}\text{\ }\text{на}\text{\ }\text{пятёрку}}\]
\[f(x) = 13x - 78\]
\[\textbf{а)}\ f(x) = 0\]
\[13x - 78 = 0\]
\[13x = 78\]
\[x = 6.\]
\[\textbf{б)}\ f(x) > 0\]
\[13x - 78 > 0\ \]
\[13x > 78\]
\[x > 6.\]
\[\textbf{в)}\ f(x) < 0\]
\[13x - 78 < 0\]
\[x < 6.\]
\[Функция\ f(x) = 13x - 78\ \]
\[является\ возрастающей,\ \]
\[так\ как\ \ \ k = 13 > 0.\]