maths-circles
2011-01-05 7:07 am
圖片參考：http://img151.imageshack.us/img151/9859/46484119.jpg
In the figure, chord CD is parallel to diameter AB.(a) Considering ⊿ABC, express y in terms of x.(b) It is given that 2(arcAC)=arcCD. Find x and y.
回答 (1)
2011-01-05 7:20 am
✔ 最佳答案
(a) Notice that ∠CDA=∠CBA=x (∠s of same segment) and ∠CDA=∠DAB=x (alt. ∠s). Also ∠ACB=90 (∠ in semi-circle)y=90-2x
(b) 2(arcAC)=arcCD =>2∠ABC = ∠CAD = y or 2x=y. With the information of (a), we find that x=22.5 and y=45
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