已知四面体ABCD的各棱长均相等,E、F分别为AB、CD的中点,求EF与AC所...

发布网友发布时间：2024-03-22 04:36

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热心网友时间：2024-03-27 22:15

取BC中点G连接EG，则∠FEG就是所求的角的大小EG=FG=1/2棱长，所以求出EF即可，连接BF，在△BEF中容易求EF，所以用余弦定理就可求角度了，这里只给你一个思路，你自己能求出来

热心网友时间：2024-03-27 22:11

One good turn deserves another　　I was having dinner at a restaurant when Harry Steele came in.
Harry worked in a lawyer's office years ago, but he is now working at a
bank. He gets a good salary, but he always borrows money from his
friends and never pays it back. Harry saw me and came and sat at the
same table. He has never borrowed money from me. While he was eating, I
asked him to lend me &2. To my surprise, he gave me the money
immediately. 'I have never borrrowed any money from you,' Harry said,'so
now you can pay for my dinner!'礼尚往来　　我正在一家饭馆吃饭，托尼.斯蒂尔走了进来。托尼曾在又家律师事务所工作，而现在正在一家银行上班，他的薪水很高，但他却总是向朋友借钱，并且
从来不还。托尼看见了我，就走过来和我坐到一张桌子前。他从未向我借过钱，但他吃饭时，我提出向他借20英镑。令我惊奇的是，他立刻把钱给了我。“我还未
向你借过钱。”托尼说道，“所以现在你可以替我付饭钱了!”