altitude h = DE sin 60 = sqrt(3)/2 * DE

please refer to

http://mathworld.wolfram.com/EquilateralTriangle.html

所有跟帖： 

• 谢谢任教授没笑话我...上几年班以后把这些知识都全部还给老师了,汗颜! -陶陶乐，乐陶陶- ♀ (20 bytes) () 12/14/2009 postreply 16:35:51

• Why didn't thank me?!!! -念亲- ♀ (208 bytes) () 12/14/2009 postreply 18:53:13

• 回复：Why didn't thank me?!!! -陶陶乐，乐陶陶- ♀ (93 bytes) () 12/14/2009 postreply 21:34:40

• 回复：回复：Why didn't thank me?!!! -陶陶乐，乐陶陶- ♀ (49 bytes) () 12/14/2009 postreply 22:11:19