（2012?杨浦区一模）已知在正四棱锥P-ABCD中（如图），高为1cm，其体积为4cm3，求异面直线PA与CD所成角的
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\u7531\u4e09\u89c6\u56fe\u53ef\u77e5\uff0c\u56db\u68f1\u9525P-ABCD\u4e2d\uff0c\u5e95\u9762ABCD\u662f\u8fb9\u957f\u4e3a1\u7684\u6b63\u65b9\u5f62\uff0cPC\u22a5\u9762ABCD\uff0c\u4e14PC=2\u2026\uff082\u5206\uff09\uff08\u2160\uff09\u7531\u9525\u4f53\u4f53\u79ef\u516c\u5f0f\u5f97VP?ABCD\uff1d13SABCD\u00d7PC\uff1d13\u00d71\u00d72=23\u2026\uff084\u5206\uff09\uff08\u2161\uff09\u8fde\u63a5AC\uff0c\u4ea4BD\u4e8e\u70b9F\uff0c\u5219F\u4e3aAC\u4e2d\u70b9\uff0c\u8fde\u63a5EF\uff0c\u5219EF\u4e3a\u4e09\u89d2\u5f62PAC\u4e2d\u4f4d\u7ebf\uff0c\u6240\u4ee5EF\u2225PA\uff0c\u53c8PA?\u5e73\u9762BDE\uff0cEF?\u5e73\u9762BDE\uff0c\u2234PA\u2225\u5e73\u9762BDE\u2026\uff086\u5206\uff09\uff08\u2162\uff09\u4ee5C\u4e3a\u5750\u6807\u539f\u70b9\uff0c\u4ee5CD\u3001CB\u3001CP\u6240\u5728\u76f4\u7ebf\u5206\u522b\u4e3ax\uff0cy\uff0cz\u8f74\u5efa\u7acb\u7a7a\u95f4\u76f4\u89d2\u5750\u6807\u7cfb\uff0c\u5219P\uff080\uff0c0\uff0c2\uff09\uff0cD\uff081\uff0c0\uff0c0\uff09\uff0cB\uff080\uff0c1\uff0c0\uff09\uff0cA\uff081\uff0c1\uff0c0\uff09\uff0c\u2234AD\uff1d(0\uff0c?1\uff0c0)\uff0cPD\uff1d(1\uff0c0\uff0c?2)\uff0cAB\uff1d(?1\uff0c0\uff0c0)\uff0cPB\uff1d(0\uff0c1\uff0c?2)\u2026\uff088\u5206\uff09\u8bbe\u9762PAD\u7684\u6cd5\u5411\u91cfn1\uff1d(x\uff0cy\uff0cz)\u7531<div style="background-image: url(http://hiphotos.baidu.com/zhidao/pic/item/a2cc7cd98d1001e9cd3ea5bbbb0e7bec54e79700.jpg); background-attachment: initial; background-origin: initial; background-clip: initial; background-color: initial; height: 5px; float: left; overflow-x: hidden; overfl
连接AC、BD交于O点，连接PO，则PO就是正四棱锥的高设异面直线PA与CD所成角的大小θ，底边长为a，
则依题意得，正四棱锥P-ABCD体积为V=
| 1 |
| 3 |
∴a=2
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