2012-II-18
答案:A
在 $\Delta BCD$ 中,
… Read 在 $\Delta BCD$ 中,
$\begin{array}{rcl}
\sin \alpha
$\begin{array}{rcl}
\sin \alpha
$\begin{array}{rcl}
\mbox{反角 } BOD & = &
留意 $OA$、$OB$、$OC$ 及 $OD$ 均為半徑,
所以,可得
$\begin{array}{rc
$\begin{array}{cl}
= & \dfrac{2}{10} \\
=
$\begin{array}{cl}
= & \dfrac{6}{20} \\
=
$\begin{array}{cl}
= & \dfr
$\begin{array}{rlllllll}
已知 $a_{18}=26$ 及 $a_{23}=61$