题目内容
数列{an}为等差数列． (1)已知数列{an}的前n项和Sn=n2+n+1． (2)已知数列{an}的前n项和Sn=n2+n．
查看答案
搜索结果不匹配？点我反馈
更多问题
6名同学分到3个班去，每班分2名，其中甲必须分在一班，乙和丙不能分到三班，则不同的分法有______．
直线(1+a)x+y+1=0与圆x2+y2-2x=0相切． (1)a=-1． (2)a=1．
Usually, there are two reasons to pursue scientific knowledge: forthe sake of the knowledge itself, and for the practical use of that knowledge.Because this second aspect of science effects the lives of most people, 31 it is much more familiar than the first. Knowledge must be gained,however, after it can be applied, and often the most important technological 32 advances arise from research pursued for its own sake.Traditionally, new technology has concerned with the construction 33 of machines, structures, and tools in a relatively large scale. The 34 development of materials for building bridges, skyscrapers or highwaysis an example of this, as it is the development of the internal-combustion 35 engine and the nuclear reactor. While such activities involve all sectionsof the sciences, the overriding goal has been the same, that is, improve 36 the human condition by finding good ways to deal with the macroscopic world. 37 Since World War Ⅱ, the focus of technological activity underwenta major change. While the old activities are still pursued, they have beenlargely superseded by applications of technology at the microscopic level.Instead of building large-scale structures and machines, modern-daytechnology tends to concentrate on finding improving ways to transfer 38 information and to develop new materials by studying the way atoms cometogether. The silicon chip and microelectronics typify this new technologicaltrend, as did the blossoming of genetic engineering. The trend can be 39 expected to continue for the foreseeable decades. 40
As anxiety-makers, examinations are second to none. That isbecause so much depends on it. They are the mark of success 21 or failure in our society. One"s whole future may be decided onone fateful day. It doesn"t matter that he wasn"t feeling verywell, or that his mother died. Things like that don"tcount on: the exam goes on. No one can give of his best when 22 he is in mortal terror, or after a sleepless night, yet this is preciselywhat the examination system expects you to do. The moment 23 a child begins school, he enters into a world of vicious competition 24 where success and failure are clearly defined and measured.Can we wonder at the increasing number of "drop-outs": young peoplewho are written off as utter failures before they have even embarked 25 a career Can we be surprised at the suicide rate among studentsA good education should, among other things, train one tothink for himself. The examination system does nothing but that. 26 What has to be learnt is rigidly laid down by a syllabus, so the studentis encouraged to memorize. Examinations do not motivate a studentto read widely, but restrict his reading; they do not enable him to seek 27 more and more knowledge, but induce cramming. They lower thestandards of teaching, for they deprive teachers off all freedoms. 28 Teachers themselves are often judged by examination results andinstead of teaching their subjects, they are reducing to training their 29 students in exam techniques which they despise of. The most 30 successful candidates are not always the best educated; they arethe best trained in the technique of working under duress.
微信支付 
支付宝支付