We assume P is a fixed point and we adjust M and N to achieve the minimum. Otherwise they all shrink to O. www.ddhw.com When the perimeter reaches the minimum, we must have 角NMO = 角NMA and 角MNO = 角MNB. Because 角NMO + 角MNO = 180° - 角AOB, we have 角NMP + 角MNP = 360° - 2 * (角NMO + 角MNO) = 2 * 角AOB. Therefore 角MPN = 180° - 2 * 角AOB. In this particular case, it is 100° This is a very nice problem with a very nice result. BTW Mr or Ms 烟, I would like to post this problem to another forum if I have your permission. I will, of course, credit it to you and this forum. www.ddhw.com
| 
哈哈哈哈 O(∩_∩)O哈哈~ 好久不来了，不小心看了一眼自己主页，发现自动关联了自己以往发过的帖，点进这个看了一眼，笑个半死。。。敢情我当初还发过这么搞笑的东西啊，我自己完全不记得了 
雷达卡
发表于 2005-1-12 18:28:04