题目

已知△ABC，若对任意，，则△ABC一定为A．锐角三角形   B. 钝角三角形   C. 直角三角形   D. 答案不确定 答案：C解析：令，过A作于D。由，推出 ,令，代入上式，得 ，即  , 也即 。从而有。由此可得 。 完形填空(共10分，每小题1分)    The word “blog” is a short way of saying web log (网络日志) .A “blogger” is a person who writes a blog 36 . Anyone can start a blog. You don't 37 be a computer expert (专家) to start your own blog.   Many people write blogs now. They share information,opinions,38 going on in their lives or anything else they want to discuss .... If you want to 39 a person's blog,the first step is to get on the Internet.Then you can search for either the blog's name 40 the person's name. After reading,you can write some comments (评价) .   Blogs are growing very fast. The number of blogs and bloggers is much 41 than before. 42 ,blogs are updated (更新) more often. Some are updated every day. Some are even updated several times a day.   Many people think that 43 blogs become more common,news reporting will depend (依赖) less on TVs or radios,but 44 on people posting news to the Internet. Then the news will be more like a conversation between reporters and readers. And blogs will attract more people 45 .() 36. A. at home   B. at school   C. on the Internet   D. on the road() 37. A. must   B. need to   C. need   D. have() 38. A. where's   B. who's   C. what's   D. how's() 39. A. read   B. write   C. hear   D. say() 40. A. and   B. or   C. also   D. to() 41. A. smaller   B. larger   C. faster   D. slower() 42. A. Anyway   B. For example   C. However   D. Moreover() 43. A. as   B. till   C. after   D. before() 44. A. little   B. less   C. much   D. more() 45. A. soon   B. also   C. as a result   D. either