→ Honor1984 : 用△CBB' ~ △ABC更好算 11/23 15:03
→ Honor1984 : B'D = BB' = 27/5 => AD = 15 - 54/5 11/23 15:05
推 brian821117 : 了解，感謝大大^^ 11/23 16:31
※ 引述《brian821117 (chaozoo)》之銘言：
: 1.
: http://ppt.cc/YAFG
過C作AB垂直線交於B'
△ACB' ~ △ABC
=> B'C = 36/5
AB' = 48/5
=> B'D = √[81 - (36/5)^2] 懶得算出來 假設為x
=> AD = AB' - x
AD + CD + AC
= AD + BC + AC
= 21 + 48/5 - x
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