答案：(a) $1$ (b) $\sqrt{3}$, $\dfrac{1}{\sqrt{3}}$
- 第二項
$\begin{array}{cl}
= & \tan \dfrac{180^\circ}{(2)+2} \\
= & \tan 45^\circ \\
= & 1
\end{array}$ - 所求的項為第一項
$\begin{array}{cl}
= & \tan \dfrac{180^\circ}{(1)+2} \\
= & \tan 60^\circ \\
= & \sqrt{3}
\end{array}$及第四項
$\begin{array}{cl}
= & \tan \dfrac{180^\circ}{(4)+2} \\
= & \tan 30^\circ \\
= & \dfrac{1}{\sqrt{3}}
\end{array}$
