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標題:
maths-circles II
發問:
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. 更新: ans係30 但我唔明點解Circumference = 6 x (360/72) = 30
最佳解答:
Let O be the centre of the circle. ∠BOC = 2∠BAC = 2 x 36° = 72° (∠ at centre) Circumference = 6 x (360/72) = 30
其他解答:
maths-circles II
發問:
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. 更新: ans係30 但我唔明點解Circumference = 6 x (360/72) = 30
最佳解答:
Let O be the centre of the circle. ∠BOC = 2∠BAC = 2 x 36° = 72° (∠ at centre) Circumference = 6 x (360/72) = 30
其他解答:
此文章來自奇摩知識+如有不便請留言告知
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
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