中五(數) 圓的基本性質吾`識... plx help

Yau

2011-09-03 7:07 pm

吾該我有d數學題吾題識敎下我.吾該

圖片參考：http://imgcld.yimg.com/8/n/HA04853099/o/701109030023713873453060.jpg

9)右圖 .ad是直徑 ab:bc:cd=1:2:3 ,求x

圖片參考：http://imgcld.yimg.com/8/n/HA04853099/o/701109030023713873453071.jpg

15) 加圖中.ab是直徑,若角acd=30度
a)求角aoc和角cob
b)求ac:cb

回答 (1)

用戶2053

2011-09-04 3:18 am

✔ 最佳答案

9) AD 是直徑 , ㄥAOD = 180°又弧AB : 弧BC : 弧CD = 1 : 2 : 3即ㄥAOB : ㄥBOC : ㄥCOD = 1 : 2 : 3設ㄥAOB = k , ㄥBOC = 2k , ㄥCOD = 3k則ㄥAOB + ㄥBOC + ㄥCOD = 180°k + 2k + 3k = 1806k = 180k = 30故ㄥBOC = 2k = 2 * 30 = 60°

15) AB是直徑 , aco = 30° , o 為圓心 :
a)OA = OC (半徑)故△OAC為等腰△得ㄥCAO = ㄥACO = 30° (等腰△ 底角)則ㄥAOC + ㄥCAO + ㄥACO = 180° (△內角和)ㄥAOC + 30° + 30° = 180° ㄥAOC = 120°ㄥAOC + ㄥCOB = 180° (平角)
120° + ㄥCOB = 180°
ㄥCOB = 60°
b)弧AC : 弧CB= ㄥAOC : ㄥCOB= 120° : 60°= 2 : 1*****************************************************************

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