第五題

(1)【黃柏榤提供】
\(\frac{\overline{AB}}{\overline{AD}} {\rm sin}^{2}{\frac{\alpha}{2}}=\frac{\overline{AB}}{\overline{AD}} \cdot (\frac{\overline{BC}}{\overline{AB}})^{2}=\frac{\overline{BC}^{2}}{\overline{AD} \cdot \overline{AB}}=\frac{\overline{BC}^{2}}{\overline{AC}^{2}}={\rm tan}^{2} \frac{\alpha}{2}\) ﹒



(2)【黃歆穎提供】

\(\frac{\overline{AB}}{\overline{AD}} {\rm sin}^{2}{\frac{\alpha}{2}}=\frac{\overline{AB}}{\overline{AD}} \cdot (\frac{\overline{AC}}{\overline{AB}})^{2}=\frac{\overline{AC}^{2}}{\overline{AD} \cdot \overline{AB}}=\frac{\overline{AC}^{2}}{\overline{AC}^{2}}=1\) ﹒