题目： 叙述并证明余弦定理。 答案： 解：余弦定理：三角形任何一边的平方等于其他两边平方的和减去这两边与它们夹角的余弦之积的两倍。或：在△ABC中，a，b，c为A，B，C的对边，有，，。证明：如下图，，即；同理可证，。
题型：填空题 根据短文内容从方框内选择正确的词，并用适当的形式填空，使短文在结构和意义上完整、通畅。do , you , happy , be , help , need , alone , have , feel , good Learners of English often ask: What are the differences between friends. Everyone ____1____ friends. We all like ___2___ close to someone. It is nice to have friend to talk and ___3___ things with. Certainly, sometimes, we need to be ___4____ . We don't always want people around. But a man will feel lonely if he ____5____ a friend. No two people are just the same . Friends sometimes don't get on ____6___ . That doesn't mean that they no longer like each other . Most of the time , they will make up and become friends again. There ___7____ more good news for people who have friends . They live longer than people who don't . Why? It could be that they are ___8____ . Being happy___9___ you stay well . Or it could be just knowing that someone cares. If someone cares about you, you take better care of ___10____. 查看答案
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