maths-circles II
2011-01-05 7:10 am
圖片參考：http://img716.imageshack.us/img716/2766/98699108.jpg
In the figure, ABC is a circle. If ∠BAC=36° and arcBC=6, find the circumference of the circle.
回答 (2)
2011-01-05 10:24 am
✔ 最佳答案
Let O be the centre of the circle.∠BOC = 2∠BAC = 2 x 36° = 72° (∠ at centre)
Circumference = 6 x (360/72) = 30
參考: micatkie
2011-01-06 1:23 am
Because angle at centre = 72, so it subtends 72/360 = 1/5 of the circumfernce.
Therefore an arc length of 6 = 1/5 x circumference
Hence circumference = 30
Therefore an arc length of 6 = 1/5 x circumference
Hence circumference = 30
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原文連結 [永久失效]:
https://hk.answers.yahoo.com/question/index?qid=20110104000051KK01485