- A sequence of terms \(a _ { 1 } , a _ { 2 } , a _ { 3 } , \ldots\) is defined by
$$\begin{aligned}
a _ { 1 } & = 3
a _ { n + 1 } & = 8 - a _ { n }
\end{aligned}$$
- Show that this sequence is periodic.
- State the order of this periodic sequence.
- Find the value of
$$\sum _ { n = 1 } ^ { 85 } a _ { n }$$