130#
大 中
小 發表於 2012-12-21 11:58 AM (第 4116 天)
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Answer
After reading the answer, I learnt how to solve the problem.
My question is, when facing such kind of question, how do we figure out that we need to draw such additional lines to solve the problem?
What would happen if the angles are not 20%, 80% and 80% respectively for triangle ACD? How can we tackle this kind of question systematically.