回複：小學生數學題 17

來源: longsky 於 2013-11-13 08:22:26 [] [舊帖] [給我悄悄話] 閱讀數 : (259 bytes)
回答: 小學生數學題 17 由 魁北克人 於 2013-11-12 18:44:56

from geometry point:

let DP perpendicular to AB, where P lies on AB. Since triangle ABC is iso-right triangle, so DP=1/2 AB = 1/ AD (as AB=AD)
Therefore, for right-triangle ADP, <DAP=30. should be easy going forward.

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