发布时间 : 星期六 文章湖南省桑植县2017-2018学年八年级数学上学期期末考试试题和答案更新完毕开始阅读
解不等式②得：x＜6， ----------5分 ∴不等式组地解集为2≤x＜6 --------6分 ∴不等式组地整数解为2，3，4，5. ---7分
23．（本大题6分） 阅读材料：
若a，b都是非负实数，则a+b≥2ab.当且仅当a=b时，“=”成立. 证明：∵(a?b)≥0，∴a－2ab+b≥0.
2
∴a+b≥2ab.当且仅当a=b时，“=”成立.
举例应用：
已知x＞0，求函数y=2x+
2地最小值. x解：y=2x+
222≥22x??4.当且仅当2x=，即x=1时，“=”成立.
xxx当x=1时，函数取得最小值，y最小=4. 问题解决：
汽车地经济时速是指汽车最省油地行驶速度.某种汽车在每小时70~110公里之间行驶时(含70公里和110公里)，每公里耗油(油量为y升.
（1）求y关于x地函数关系式(写出自变量x地取值范围)；
（2）求该汽车地经济时速及经济时速地百公里耗油量(结果保留小数点后一位). 解：（1）y关于x地函数关系式:
1450+)升.若该汽车以每小时x公里地速度匀速行驶，1小时耗18x21450x450y?(?2)?x??,70?x?110-------3分
18x18x（2）由（1）有：
y?(1450x450x450?2)?x???2??2?5?10， 18x18x18x当且仅当
x450时，即x?90时，“=”成立。 ?18x经济时速为90公里/小时。 经济时速地百公里耗油量： 当x?90时，每公里耗油为：
14501111450?2???（升） +2=
18901818918x1?100?11.1(升）. 9经济时速地百公里耗油量(结果保留小数点后一位)为：
答：经济时速为90公里/小时，经济时速地百公里耗油量为11.1升。
--------6分 点评：
本题考查了分式乘法，二次 根式 地乘法运算，分式方程地解法，分析问题，处理问题，解决实际问题地能力。
赠送—初中英语总复习知识点归纳 并列句 and 和，并且， work hard, and you can pass the exam.but 但是 he is rich but he is not happy. Or 否则，要不然，或者（在否定句中表和） Hurry up, or you’ll be late. so 因此，所以 Kate was ill so she didn’t go to school. For 因为 I have to stay up late, for I have a lot of work to do. 状语从句 当状语从句的引导词为If, when, before, after, until, as soon as 等，主句和从句有下列情况： 英语句子中如果一看到 Thought----but----; because----so---这种结构,就是错误.倒装句 so+助动词\\BE动词\\情态动词+另一主语，表示后者与前者一致。so+上句主语+助动词\\BE动词\\情态动词，真的，确实如此。 Tom watched TV last night, so did Ann. Tom didn’t watch TV last night. Neither did Ann. ---You’ve left the light on. ---So I have. I’ll go and turn it off. 宾语从句 ?从句用陈述句语序。?主句与从句的关系。 A．主现从不限；B．主过从过； C．真金不怕火炼。The earth moves around the sun. ③常见的宾语从句。 She says that ---- I hope / think / feel / wonder---- I wonder if he will join us in the discussion tonight. Could you tell / show me--- Could you please tell me where the teacher’s office is? Do you know---- Do you know where Mr. Li lives? Please tell me --- She asked me --- I don’t know ---- I don’t know whether Tom will go or not.定语从句 that和which在指物的情况下一般都可以互换, 但在下列情况下, 一般用that而不用which。 (1) 先行词为all, everything, nothing, something, anything, little, much 等不定代词时。 I am sure she has something (that) you can borrow. (2)先行词被all, every, no, some, any, little, much等修饰时。I’ve read all the books that are not mine. (3)先行词被序数词或最高级修饰时。This is the first book (that) he has read. (4)先行词被the only, the very, the same, the last修饰时。 This is the very book that belongs to him.一般用that而不用who (1) 先行词是who或who引导的主句。 Who is the girl (that) drove the car? Who (that) broke the window will be punished. (2) 主句以There be 引导时 。 There are 200 people (that) didn’t that和which在指物的情况下一般都可以互换, 但在下列情况下, 一般用which而不用that。 (1)关系代词在限制性定语从句中紧跟介词作宾语（介词提前）。 Those are many trees under (which) they can have a rest. (2) 在非限制性定语从句中。 Football , (which) is a very popular game, is played all over the world. 后跟ing 的词有Finish doing Before 2008 Beijing we will finish building the Olympic Park. enjoy doing 喜欢做某事 I enjoy reading English loudly.
mind doing 介意（反对）做某事 would you mind opening the window? practice doing sth. 练习做某事 we should practice speaking English as often as possible. be busy doing sth. 忙于做某事 be worth doing sth. 值得做某事 feel like doing sth =want to do sth. 想要做某事spend --- (in) doing sth 花费时间做某事 stop / prevent / keep ----from doing 阻止某人做某事have trouble \\problem / a hard time doing sth. 做某事很困难 Have fun doing sth. =have a good time doing sth. 做某事很快乐go on doing sth 接着做原来做着的事 go shopping / swimming/ skating /surfing---do some running / washing/ cooking --- 介词(for, with, without, about ---) 后跟动词原形:why don't you why not you'd better (not) would you please (not) make\\ let \\ have\\ [注意: 在被动语态中, t o 要加上]