题干

关于x的一元二次方程(a+1)x2-4x-1=0有两个不相等的实数根,则a的取值范围是(  )

A:a>-5且a≠-1

B:a≠-1

C:a>-5

D:a>5

上一题 下一题 0.0难度 选择题 更新时间:2012-04-25 12:18:19

答案(点此获取答案解析)

B

同类题3

Section A

Directions: Read the following passage. Fill in the numbered blanks by using the information from the passage.

Write NO MORE THAN THREE WORDS for each answer.

    Since the earliest civilizations, people have controlled rivers to meet society's demands. Today, rivers are controlled for many reasons, primarily to maintain reliable water supplies for daily, agricultural and industrial needs, for power generation, for navigation (航行), and to prevent flooding.

    River control is achieved by channelization, a term that covers a range of river engineering works, including widening, deepening, straightening and stabilization of banks, and by the construction of dams.

    An important period of channelization took place in Europe during the l9'th century, when many large rivers were straightened and their beds deepened. One of the most dramatically changed was the Tisza River, a branch of the Danube that flows through Hungary. The controlling of the Tisza, designed to reduce flooding and make land for agriculture, included cutting off more than 100 meanders (河曲), shortening the river's length by nearly 400 kilometers.

    One of the most common ways in which people control rivers is by damming them. The past 50 years or so has seen an increase in dam construction worldwide, and at the beginning of the 21st century, there were about 800,000 dams globally, some towering more than 200 meters in height.

Despite their successes, many dams also cause significant environmental changes that prove harmful. Some particularly deep reservoirs (水库) can bring about earthquakes due to the stress on their bottom rocks caused by huge volumes of water. Downstream of a reservoir, the river is certainly influenced in many ways: water volume, speed and quality are all affected, leading to changes in the landscape and among plants and animals.

⑴____ ⑵____ ⑶____ ⑷____ ⑸____ ⑹____ ⑺____ ⑻____ ⑼____ ⑽____ 

同类题4

积极关心社会的变化发展是我们青少年健康成长的迫切要求。盐城市某初级中学九年级成立专门小组,开展主题实践探究活动。假如你是该班的一员,请你一起参与探究和实践。

【我思考】第一小组同学通过上网获得以下一则材料:

表二:2010年-2014年上半年三大产业的比值

类别|年份

2010年

2011年

2012年

2013年

2014年

第一产业

10.2

10.1

10.1

10

7.4

第二产业

46.8

46.8

45.3

43.9

46

第三产业

43

43.1

44.6

46.1

46.6

注:第一产业包括农业、林业、牧业和渔业;第二产业包括制造业、采掘业、建筑业和公共工程等部门;第三产业除第一、第二产业外的其他产业,包括新兴产业。

材料三:2014年,我国农村居民人均可支配收入10489元,实际增长率9.2%;城镇居民人均可支配收入28844元,实际增长6.8%。

【我分析】材料二:2015年12月31日,***主席在2016年新年贺词中提到:有付出,就会有收获。2015年,中国人民付出了很多,也收获了很 多。我国经济增长继续居于世界前列,改革全面发力,司法体制改革继续深化,“三严三实”专题教育推动了政治生态改善,反腐败斗争深入进行。经过全国各族人 民共同努力,“十二五”规划圆满收官,广大人民群众有了更多获得感。

【我践行】材料三:2015年12月12日屠呦呦在诺贝尔奖颁奖仪式中致辞道:“我因发明青蒿素而获奖。这不仅是授予我个人的荣誉,更是中国中医的荣誉, 每每遇到研究困境时,我就一遍又一遍温习中医古籍,中国医药学是一个伟大的宝库。我代表中国,代表中国中医和中国科学家。我要感谢当年从事523抗疟研究 的中医科学院团队全体成员,感谢全国523项目单位的通力协作。但我不是以获得诺贝尔奖为终极目的,在我的科研生涯中,一代又一代,一茬又一茬的青蒿(中 国中医药研究工作者)‘前赴后继’,奉献了自己的身驱,成就了中国的中医事业。正是因为他们的牺牲,才铺就了我通往诺贝尔的坦途。”