※ 引述《bfl821002 (章魚哥)》之銘言：
: https://i.imgur.com/8wkE04V.jpg
: 第七題
: 如題，這題該怎麼破題完全沒想法
: 有大大能解謎嗎
∠MAB = a
∠CMA = b
=> ∠MBC = a - b
∠MCB = a
延長BC至C'使∠C'MC = ∠AMC
=> ∠MC'B = a - b = ∠MB
=> MC' = MB = MA
=> △MC'C = △MAC (SAS)
=> CC' = CA
=> BD = DC' = DC + CA
= 2 + 1
= 3
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