推 wayne2011 : 蠻接近ch.27th當中的解法8,因為都有提到"等邊"三角. 07/28 16:55
→ Honor1984 : 哪本書的chap27? 07/28 17:16
推 wayne2011 : FAlin當初提到的"幾明",寫到最後角度竟然也都1/2倍. 07/28 18:13
※ 引述《tcbt32 (唐)》之銘言：
: 10
: http://imgur.com/9RxAbwf
: 麻煩各位大大了
∠BAN = 50, ∠B = 80
=> ∠BNA = 50
=> BN = BA
在CN上找一點N'使得∠N'AB = 60
AN'交BM於O
N'M = MO ------(1)
則OB = OA = AB => OB = BN
又∠NBO = 20
=> ∠NOB = 80, ∠ONA = 30
=> ∠N'ON = 40
又∠BN'O = 40
=> NO = NN' ---------(2)
由(1)(2)
=> ∠N'MN = ∠OMN
=> ∠NMB = 60/2 = 30
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