回復 1# P78961118 的帖子
\(\overline{AC}=\sqrt{3},\angle BCA={{90}^{{}^\circ }}\)
\(C\left( 0,0,0 \right),B\left( 0,0,1 \right),A\left( \sqrt{3},0,0 \right)\)
\(D\)在圓\(C:{{\left\{ \begin{align}
& {{x}^{2}}+{{y}^{2}}=\left( \frac{\sqrt{3}}{2} \right) \\
& z=0 \\
\end{align} \right.}^{2}}\)上移動
易知當\(AD\)是圓\(C\)之切線時,\(\angle DAC\)有最大值30度
[ 本帖最後由 thepiano 於 2017-3-22 22:39 編輯 ]