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👨🏻‍🏫 學術台數學

一個青檸

2012-04-24 3:47 am

圖片參考：http://imgcld.yimg.com/8/n/HA01076848/o/701204230069213873398430.jpg

AB = BC = CA = AD，求 ∠BDC。

回答 (3)

用戶2053

2012-04-24 8:19 am

✔ 最佳答案

設∠ABD = ∠ADB = k
則∠DBC = 60° - k
∠ACD = ∠ADC = k +∠BDC
△BCD內角和 = ∠DBC + ∠ACB + ∠ACD + ∠BDC = 180°
60° - k + 60° + k +∠BDC + ∠BDC = 180°
∠BDC = 30°

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一個青檸

2012-04-24 6:10 am

I also thought that. But this is just a F.1 questions (taken from http://www.hcm.org.hk/index.html), do we have a easier to do it (not easy, simple)?

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用戶27207

2012-04-24 5:59 am

30
(by a bit circle geometry)

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