\[\boxed{\mathbf{779}\mathbf{.}}\]
\[s(t) = 0,25t + 2\]
\[1)\ От\ t_{1} = 4\ до\ t_{2} = 8:\]
\[v_{ср} = \frac{s\left( t_{2} \right) - s\left( t_{1} \right)}{t_{2} - t_{1}} =\]
\[= \frac{0,25 \bullet 8 + 2 - 0,25 \bullet 4 - 2}{8 - 4} =\]
\[= \frac{2 - 1}{4} = \frac{1}{4} = 0,25.\]
\[Ответ:\ \ 0,25.\]
\[2)\ t_{1} = 4\ и\ t_{2} = 8:\]
\[v = \lim_{h \rightarrow 0}v_{ср} = \lim_{h \rightarrow 0}{0,25} = 0,25\]
\[v(4) = 0,25\]
\[v(8) = 0,25.\]
\[Ответ:\ \ 0,25.\]