h*l
发帖数: 19 | 1 正弦，余弦，最后万能代换！ （呵呵，也有点尉迟恭的感觉，
why?）
手工计算是非常简单的，ti＝tan（Ai/6)，没有把握的同学可
以用一下另三板斧：积化和差，三倍角公式与对称化。（呵呵，
也有点罗成的“梅花七蕊”的感觉。）
最后还没把握的，就拿出秦叔宝的“杀手锏” －－ Mathematica！
大致上是一些如：sin((pi-B)/3)*sin((pi+B)/3)*sin(c)*...
cos(...) / ...的项。。。 | h*l
发帖数: 19 | 2 Really, where is the #? I actually don't have much
time now, hehe.
By the way, the proof below is actually calculated
by me via hand for fun. So, it's not a joke. And
the calculation is not hard.
A conclusion is although trigonomy technique was
usually consider to be not wize for middle level
Euclid geometry problem, this view is COMPLETELY
mechanically changed now. The tg(t/2) method is
almost always straightforwards without much calculation.
But one problem is it's still "直观“，so some time
we h |
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