2015年8月5日 星期三

訓練數學感 71 ─ 世界上最難的簡單幾何題

http://4rdp.blogspot.com/2015/08/71.html

小朋友假日吵著要網路連線,只好出這道最近蠻紅的幾何題,讓他想一想,居然用觀察法花 50 分鐘算出答案!

求角 AED 多少度?

題目原文如下:

Using only elementary geometry, determine angle x. Provide a step-by-step proof.

You may only use elementary geometry, such as the fact that the angles of a triangle add up to 180 degrees and the basic congruent triangle rules(side-angle-side, etc.). 

You may not use more advanced trigonomery, such as the law of sines, the law of cosines, etc. There is a review of elementary geometry below.

This is the hardest problem I have ever seen that is, in a sense, easy. It really can be done using only elementary geometry. This is not a trick question.

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