题目

（1）若x＜5,n∈N,则下列不等式：①|xlg|＜5|lg|;②|x|lg＜5lg;③xlg＜5|lg|;④|x|lg＜5|lg|.其中，能够成立的有___________.（2）不等式≥1成立的充要条件是___________。 答案：思路解析：（2）题求充要条件，因而可从不等式的性质|a+b|≥|a|-|b|出发，去寻找原不等式成立的充要条件.(1)∵0＜＜1,∴lg＜0.由x＜5，并不能确定|x|与5的关系，∴可以否定 ①②③，而|x|lg＜0,④成立.（2）当|a|＞|b|时，有|a|-|b|＞0,∴|a+b|≥||a|-|b||=|a|-|b|,∴必有≥1.即|a|＞|b|是≥1成立的充分条件.当|≥1时， Successful films and TV programs make large amounts of money, and so do the performers who appear in them. A few big shows can make a rock musician a millionaire（百万富翁） in a very short time. High art, however, has serious financial（财政的） problems. It costs more to put on an opera（歌剧）concert, or ballet（芭蕾） than the sale of tickets can bring in. Men and women interested in high art are always being asked to give money to make future performance possible. Small government subsidies（津贴） have also helped to support the arts in the last few years. 56. It is easier for ______ to make money.   A. an opera performer          B. a pianist     C. a ballet actor               D. A rock musician 57. High art has financial problems because ________. no people would offer money for it       it is not supported by the government it cost much but not many people enjoy it  prices of tickets for it are not high enough 58. The government has given ________ money to support _______ in the last few years.   A. a large amount of… high art              B. a small amount of… high art   C. little… all kinds of art                   D. plenty of… popular art 59. From the passage we can concluded (推断) that ________. A. high art is not enjoyed by young people B. successful films and TV programs are called high arts C. all people enjoy popular art instead of high art D. most people like popular art better than high art