ohe09nz81r的部落格

標題:

circle

發問:

圖片參考：http://img805.imageshack.us/img805/8555/14089568.jpg In the figure, ABCD is a circle. AB produced and DC produced meet at E. If AC and BD intersect at F, then angleABD=?

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最佳解答:

Let ∠ABD = x, then ∠ACD = x (∠ in the same segment) ∠ABD + ∠BAF = 82 (Ext. ∠ of triangle) ∠BAF = 82 - x ∠CDF = ∠BAF = 82 - x (∠ in the same segment) With ∠BAF + ∠CDF + BEC = ∠AFD: 82 - x + 82 - x + 30 = 82 2x = 112 x = 56

其他解答:

i give alternative solution, hope it is helpful http://www.webpagescreenshot.info/img/664187-611201143542pm.png 圖片參考：http://www.webpagescreenshot.info/img/664187-611201143542pm.png