\[\boxed{\mathbf{784}\mathbf{.}}\]
\[s(0) = 0\]
\[s(1) = 1,5\]
\[s(2) = 2,5\]
\[s(3) = 3.\]
\[\textbf{а)}\ \lbrack 0\ 1\rbrack:\]
\[v_{ср} = \frac{s(1) - s(0)}{1 - 0} =\]
\[= \frac{1,5\ - 0}{1} = 1,5\]
\[\textbf{б)}\ \lbrack 1\ 2\rbrack:\]
\[v_{ср} = \frac{s(2) - s(1)}{2 - 1} =\]
\[= \frac{2,5 - 1,5}{1} = 1\]
\[\textbf{в)}\ \lbrack 2\ 3\rbrack:\]
\[v_{ср} = \frac{s(3) - s(2)}{3 - 2} =\]
\[= \frac{3 - 2,5}{1} = 0,5.\]