\[x² - x - q = 0;\ \ \ x_{1} - x_{2} = 4\]
\[По\ теореме\ Виета:\]
\[\left\{ \begin{matrix} x_{1} + x_{2} = 1 \\ x_{1} - x_{2} = 4 \\ \end{matrix} \right.\ \text{\ \ }( + )\]
\[2x_{1} = 5 \Longrightarrow x_{1} = 2,5\]
\[x_{2} = 1 - x_{1} \Longrightarrow x_{2} = 1 - 2,5 =\]
\[= - 1,5\]
\[x_{1} \cdot x_{2} = q\]
\[2,5 \cdot ( - 1,5) = 3,75 = q\]
\[Ответ:x_{1} = 2,5;\ \ x_{2} = - 1,5;\ \ \]
\[q = 3,75.\]