\[\boxed{\mathbf{917}\mathbf{.}}\]
\[1)\ a = - 1,\ \ \ b = 7:\ \ \]
\[f( - 1) = 0,\ \ \ \]
\[f(7) = - 2,\ \ \ \]
\[f^{'}(4) = 0.\]
\[f^{'}(x) > 0\ при\ - 1 < x < 4;\ \ \ \]
\[f^{'}(x) < 0\ при\ 4 < x < 7.\]
\[2)\ a = - 5,\ \ \ b = 4:\ \ \ \]
\[f( - 5) = 1,\ \ \ \]
\[f(4) = - 3,\ \ \ \]
\[f^{'}( - 1) = 0.\]
\[f^{'}(x) < 0\ при\ - 5 < x < - 1;\ \ \ \]
\[f^{'}(x) > 0\ при\ - 1 < x < 4.\]