\[\boxed{\mathbf{785}\mathbf{.}}\]
\[s(0) = 2\]
\[s(2) = 1\]
\[s(3) = 3\]
\[s(3,5) = 4.\]
\[\textbf{а)}\ \lbrack 0\ 2\rbrack:\]
\[v_{ср} = \frac{s(2) - s(0)}{2 - 0} = \frac{1 - 2}{2} =\]
\[= - \frac{1}{2} = - 0,5\]
\[\textbf{б)}\ \lbrack 2\ 3\rbrack:\]
\[v_{ср} = \frac{s(3) - s(2)}{3 - 2} = \frac{3 - 1}{1} = 2\]
\[\textbf{в)}\ \lbrack 3\ 3,5\rbrack:\]
\[v_{ср} = \frac{s(3,5) - s(3)}{3,5 - 3} =\]
\[= \frac{4 - 3}{3,5 - 3} = \frac{1}{0,5} = 2.\]