Maths -- circle urgent

用戶25529

2011-05-01 12:56 am

Can anyone help me for the following th\wo questions :

圖片參考：http://imgcld.yimg.com/8/n/HA00656648/o/701104300089013873432450.jpg

** Point O is the center of the circle

更新1:

幅圖太大，可以save 落電腦睇

更新2:

24b 點解 ∠ECD = ∠EAB + ∠AEC = 75 之後可以 arc EB : arc BD = 4 : 1

更新3:

30 唔太明，可唔可以詳細D

更新4:

THX, 可唔可以幫我做埋呢條 http://hk.knowledge.yahoo.com/question/question?qid=7011050100566&mode=w&from=question&recommend=0&.crumb=TeD/nYJ.SFO

回答 (1)

myisland8132

2011-05-01 2:12 am

✔ 最佳答案

24(a) ∠EAB = 4∠AEC = 60(b) ∠ECD = ∠EAB + ∠AEC = 75So, arc EB : arc BD = 4 : 130 ∠OSR = θ => ∠ROS = 90 - θ/2∠ORP = [180 - (90 + θ/2)]/2 = 45 - θ/4∠PRS = 45 + 3θ/4 <= 90So, 0 <= θ <= 60

2011-05-01 00:08:20 補充：
因為圓周角和弧長成正比

我覺得第30條個θ其實是定值

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