悠闲数学娱乐论坛(第3版)»论坛 › 数学区 › 初等数学讨论 › 立体几何

Return to list New

View: 1785|Reply: 3

[几何] 立体几何

[Copy link]

182 Threads	197 Posts	1972 Credits

Credits: 1972

Send PM

guanmo1 Post time 2015-11-2 22:41 |Read mode

立体几何.jpg

Reply

730 Threads	110K Posts	910K Credits

Credits: 93643

Send PM

kuing Post time 2015-11-2 22:49

作 AB 上的高 CH，只要 $\angle BCD\geqslant \angle HCD$ 即可，下略

Reply

182 Threads	197 Posts	1972 Credits

Credits: 1972

Send PM

Author| guanmo1 Post time 2015-11-3 16:27

回复 2# kuing

简洁有力！

Reply

211 Threads	944 Posts	6197 Credits

Credits: 6197

Send PM

敬畏数学 Post time 2015-11-4 09:25

取BC中点E，只需ADE为等腰三角形，或者BC在ACD所在平面上，构成ABDC棱长为1锐角为60°的棱形。答案A。
此题选择题，直接否定BCD。不可能大于等于2.

Reply

Return to list New

手机版|悠闲数学娱乐论坛(第3版)

2025-3-6 17:53 GMT+8

Powered by Discuz!

× Quick Reply To Top Return to the list