2012+2012²-2013²用提公因式法怎么解

请去文库看：
http://wenku.baidu.com/link?url=xxv-a90g-GnslXGhXsEbLqut_SU9e0pSeKqSheNshV2V1nf4TTtKDz-3PwIY6VMe1B04XoKndjds3eZ6bZ634yrcTvb55Gg_cp_SUxAiyRy

(1-2)×(2-3)×(3-4)×…×(2012-2013)
=（-1）×······×（-1） （共2012个-1相乘）
=1

证明：因为∠1=∠2
所以∠1+∠BAC=∠2+∠BAC,即∠EAC=∠DAB
又因为AD=AE,AC=AB
所以△EAC全等于△DAB
所以∠3=∠4.

找数学老师要,一般会给你们参考的

周报求答案很少人回答！也没什么人知道，以前就答案免费，现在要钱。还是别花费这些时间了，自己做吧！不行就回去抄同学咯！

最后一问
③S=（t+2）8/t-8-1/2×2×（8/t-8/（t+2））=16t+16/t^2+2t

逆战高手加我

选择题：ADDCD CBBBA BCBAD B

每个学校试卷都不一样

答案还要吗?到第49期的答案都有,我们发到第50期了

http://wenku.baidu.com/view/d26bf7826529647d2728526d.html不知是不是

二．根据读音规则,判断下列各组单词中,哪一个单词划线部分的读音与其它三个划线部分的读音不同,请选出.（共5分,每小题1分）
（ ）1. A. hand B. cake C. map D. bag
（ ）2. A. red B. bed C. me D. let
（ ）3. A. bread B. meat C. tea D. eat
（ ）4. A. car B. far C. warm D. hard
（ ）5. A. go B. dog C. good D. orange
三．词汇（A、B两部分共10分,每小题1分）
（A）选择与句中划线部分意思相同或相近的解释.
（ ）1. I hope you’ll have a good time at the party.
A. enjoy yourself B. study well C. hurry up
（ ）2. Will you take care of Polly when we are away on holiday?
A. wait for B. look after C. laugh at
（ ）3. Tere are a lot of apples on the trees.
A. few B. many C. no
（ ）4. Mike went to the Great Wall with his parents.
A. boy and girl B. brother and sister C. father and mother
（ ）5. I find it hard to learn English well.
A. difficult B.cheap C. careful
（B）用括号内所给单词的适当形式填空.
6. How many __________________are there in your class?（girl）
7. Where is Lucy? Lily is looking for __________________ （she）
8. Li Ming is ______________________ than Chen Hua. （tall）
9. October is the ______________________ month of the year. （ten）
10. Which is the ______________________skirt of the three? （beautiful）
四．选择填空（共20分,每小题1分）
从下列各题所给的四个选项中,选择最佳答案.
（ ）1. It’s hot ____________summer in Beijing.
A. by B. on C. at D. in
（ ）2. I met Kate on ___________way home yesterday.
A. my B. me C. his D. him
（ ）3. Bruce, look at your dirty shoes. You’d better ____________them right now.
A. washed B. washing C. wash D. to wash
（ ）4. “Whose bike is it ?” “It’s ____________”
A. John B. John’s C. Johns’ D. Johns
（ ）5. “Can you sing the song in English?” “No,I _________”
A. may not B. mustn’t C. needn’t D. can’t
（ ）6. The doctor often tells him _____________ more exercise.
A. to take B. taking C. taken D. take
（ ）7. “What did you do last night?” “I did my homework and
______________TV.”
A. watch B. watched C. will watch D. am watching
（ ）8. The Whites _____________many places of interest since they
came to China.
A. have visited B. will visit C. visited D. visit
（ ）9. I’m hungry. Please bring me some ______________.
A. kites B.desks C. boxes D. cakes
（ ）10. Most of the children enjoy _____________ computer games.
A. play B. playing C. played D.to play
（ ）11. This is Miss Gao. She _________your new teacher.
A. be B. am C. is D.are
（ ）12. He has two basketballs. One is new, ___________ is old.
A. the other B. other C. the others D. others
（ ）13. “ ____________ were you born?” “On May 12, 1985”.
A. What B. Which C. When D.where
（ ）14. “Can you ______________ Chinese, Mr Smith?” “Yes, but just
a little.”
A. talk B. speak C. tell D. say
（ ）15. Which is smaller, the sun _____________the moon?
A. so B. but C. or D. and
（ ）16. Don’t forget to turn_____________TV before you go to bed.
A. off B. to C. on D. and
（ ）17. “She didn’t come to school yesterday, did she?”
“______________”, though she was not feeling very well.”
A. NO, she didn’t
B. Yes, she didn’t
C. No, she did D. Yes, she did
（ ）18. “I’m going to Hang Zhou for a holiday this weekend.”
“____________, you are there, can you buy me some green tea?”
A. Because B. If C. While D. After
（ ）19. “When shall we meet again next week?”
“______________ day is possible. It’s no problem with me.”
A. Either B. Neither C.Every D. Any
（ ）20. There is not enough _____________ in the corner to put the
table.
A. place B. room C. floor D. ground
五．根据汉语意思完成下列各句.每空只填一词.（共10分,每空1分）
1．我们该去吃晚饭了.
It’s time ________ us _________ have supper.
2．这座楼房和那座楼房一样大.
This building is as________ ________ that one.
3．如果你不早起,上学就会迟到.
_________ you don’t get up early, you’ll _______ late for
school.
4．王力跑得如此快,以致于我赶不上他.
Wang Li ran ________ fast _______ I couldn’t catch up with him.
5．昨天他直到做完作业才去睡觉.
He did _________ go to bed _________ he finished his homework
yesterday.
六．补全对话（A、B两部分共15分,每空1分）
（A）根据对话内容,在每个空白处填入一个适当的词,使对话完整,合乎情景.
A：Hello, 954121
B：Hello! Is (1) ____________ Tom?
A：Yes, speaking.
B：Tom, this is Jack. Fred is (2) ___________ in hospital
A：Oh, I’m (3) __________ to hear that.
B：I want to (4) ___________ him, Do you know the (5)________ to the North Street Hospital?
A：Yes. You can take the No. 27 bus. Get (6) __________at the North
Street. Then (7)________ along the road, take the first turning (8)
__________
the right. Walk on and (9) _______ left. You’ll find (10) ________ in
fornt you.
B：Thank you very much.
（B）根据对话内容,选择方框中适当的句子,使对话完整、通顺.
Lin Tao：Hi, Sam! How are you today?
( ) Sam： 11 What about you?
Lin Tao：I’m OK. Are you free tomorrow?
( ) Sam： 12
Lin Tao：We’re going to have a swim.
( ) Sam： 13 Can I come?
( ) Sam： 14
Lin Tao：We are going to meet outside the school gate, at two o'clock.
( ) Sam：OK. 15
A．Fine, thanks.
B. How much is it?
C. Where are you going to meet?
D. Yes. Why?
E. Goodbye!
F. Good idea!
七．阅读理解（共30分,每小题2分）
阅读下面三篇短文,根据其内容从各题所给的四个选项中,选择最佳答案.
（A）
The students were having their chemistry（化学）class. Miss Li was telling the children what water was like. After that, she
asked her students, “What'swater?" No one spoke for a few minutes.
Miss Li asked again, "Why don't you answer my question?Didn't I tell you what water is like?"
Just then a boy put up his hand and said,“Miss Li, you told us that water has no colour and no smell. But where to
find such kind of water? The water in the river behind my house is always
black and it has a bad smell.” Most of the children agreed with him.
“I’m sorry, children.”said the teacher, “Our water is getting dirtier and dirtier. That’s a pro
blem.”
( ) 1. The students were having their __________class.
A. Eglih B. Chinese C.chemisty D.maths
( )2.Miss Li was telling the chldren what __________ was like.
A. water B. air C. earth D. weather
( )3. A boy said, “The water in river behind my house is always __________”.
A. white B. black C. clean D. clear
( )4. Most of the children __________ the boy.
A. agreed with B. wrote to C. heard from D. sent for
( ) 5. The water in the river has colour and smell because it is
getting _________
A. more and more B. less and less
C. cleaner and cleaner D. dirtier and dirtie

A.2x-(32-x)≥48
B.2X+(32-X)≥48
C.2X+(32-X)≤48
D.2X≥48

解题思路：

2014×2012−20132=(2013+1)(2013−1)−20132=20132−1−20132=−1，

    


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很高兴为您回答.因没有题目内容,还是亲自做吧.网上（如：百度文库、中学学科网）可能查找到一些答案,一般不全.对搞不懂的题目,可以上传题目内容以方便为你回答.

天津14个区

an=n,当n=k
an=-1,当n=k+1
k={1,2,3,...}
k为从1开始的自然数

18.（1）p或q:根号二是无理数或小于1（真命题） p且q:根号二是无理数且小于1（假命题） 非p:根号二不是无理数（假命题） 19.（1）（2）是全称命题,（3）（4）是特称命题.（1）∵a的x次方＞0（a＞0且a≠1）恒成立,∴命题（1）是真命题.（2）存在x1＝0,x2＝pai,x1＜x2,但tan0==tanpai,∴命题（2）是假命题.（3）y=绝对值sinx是周期函数,pai就是它的一个周期,∴命题（3）是真命题.（4）对任意x∈R,x² 1＞0,∴命题（4）是假命题 20.命题p是真命题,∴0＜m＜6,m∈正整数.①A＝｛x1（mx-1）/x＜0｝=｛x10＜x＜1/m｝,B=｛x1㏒1/2x＞1｝=｛x10＜x＜1/2｝,∴命题q是真命题,∴B是A的真子集,则1/m＞1/2,②由①②得m=1.

=（1+2-3）+（4+5-6）+（7+8-9）+…+（2011+2012-2013）
=0+3+6+……+2010 （共671个）
=2010×671÷2
=674355

因为AD//BC
所以∠ADB=∠CBD
则∠ADB-∠ADE=∠CBD-∠CBF
所以∠EDB=∠FBD
则DE//BF
所以∠E=∠F

111

(提供邮箱,我可以把解析发给你)


高三新课程第18期答案
综合技能强化训练（17）
1-5 BCACA 6-10 ABABB
11-15 ACBCA 16-20 CCBBA
21-25 ADDAB 26-30 DBCDC
31-35 BDACD 36-40 ABDBC
41-45 ABDBC 46-50 DBABD
51. Let me show you out
52. Remember me to your mother
One possible version:
Dear fellow students,
As we all know, middle school students today don’t have enough time to read extracurricular books. A recent research shows that 72.27% of middle school students read less than 10 extracurricular books in a year. 5.94% of them don’t do any extracurricular reading in a year. What’s worse, only 15.5% of students have ever read the four masterpieces of China. This situation is so worrying that I suggest we should do something to improve it.
First of all, we should spend less time watching TV or surfing the Internet so that we can have more time for reading. Besides, we should read more classic books because they are beneficial to us in many aspects.
In conclusion, let’s devote more time to reading and enjoy the pleasure brought by books. Let’s start from now on!
阅读理解专项突破（17）
1-5 DCDBD 6-10 ADDBD
11-15 ABACA 16-20 BBCDC

高三新课程第19期答案
综合技能强化训练（18）
1-5 ABACB 6-10 ABACB
11-15 CABCB 16-20 BACCA
21-25 BACBD 26-30 ACBDA
31-35 CABDC 36-40 BDDAB
41-45 CDBBA 46-50 DCBAC
51. Anyone can make a mistake
52. It’s the least I can do
One possible version:
A discussion has been held among us about whether to study at home or abroad after graduation from senior high school.
Some prefer to study abroad. They believe that by studying abroad, students can broaden their horizons and improve their language skills. What’s more, students can become more independent. However, some think it better to study at home. For one thing, life at home is more convenient and students don’t have to spend too much money. For another, studying at home helps students adjust to college life more quickly.
In my opinion, we should make decisions according to our situations and interest. As long as we try hard, we will have a bright future whether at home or abroad.
阅读理解专项突破（18）
1-5 CBBCC 6-10 BDAAB
11-15 CCDBC 16-20 DCADC

很高兴为您解答!
八年级课程导报数学上册人教精华第14期2版2012-2013学年学年答案：
1．D．2．D．3．B．4．D．5．D．6．B．7．A．8．A．9．B．10．C． 二、∵∠BAC＝90°,∴∠CAH+∠BAM＝90°.∵AM⊥BD,∴∠DBA+∠BAM＝90°.∴∠CAH＝∠DBA.又∵AC＝AB,∴△BDA≌△ACH.∴∠BDA＝∠H,CH＝AD.又∵AD＝CE,∴CH＝CE.
11． ± ．
3．
∵AB＝AC,∠BAC＝90°,∴∠ACB＝45°,∴∠HCN＝45°,∴∠ECN＝∠HCN.∴△ECN≌△HCN.∴∠H＝∠NEC.∴∠BDA＝∠NEC.∵∠BDA＝∠EDF,∠NEC＝∠DEF,∴∠EDF＝∠DEF.(2) ∠EDF＝∠DEF.证明方法同（1）.(3) ∠EDF＝∠DEF.证明方法同（1）.26． ． （1）① = ； = ； ②所填的条件是：∠α
12．答案不唯一,如∠A=∠C,∠B=∠D,OD=OB,AB∥CD． ． 13．-1． 14．50°或 80°．15．点 B ．16．等边． ． ． ． 17．22.5°．18．①②③． 17 三、 19． （1） −1 ； （2） 1 ． 20．证明：∵AB＝BC,BD⊥AC,∴∠ABD＝∠DBC.∵DE∥BC,∴∠EDB＝∠DBC.∴∠EDB＝∠ABD.∴ED＝EB.∴△BDE 是等腰三角形.21．(1)A′(
3 ,3 ),B′( 3 − 1 ,0)；(2)3 ．
22．Rt△AEF≌Rt△FBA．提示：可用 HL 证明． 23.（1）过 A 作 AE⊥MN,垂足为点 E.在 Rt△BCO 中,∵∠BOC=30°,∴BO=2BC=6km.∵AB=10km,∴OA=16km.∴AE=8km.（2）提示：作出点 A 关于 MN 的对称点 K,连接 BK 交 MN 于点 P,则点 P 就是新开发区的位置,画图略.24． （1）通过猜想、测量或证明等方法不难发现∠BQM=60°． （2）成立,证明：∵△ABC 为等边三角形,∴AB=AC,∠BAC=∠ACB=60°,∴∠ACM=∠BAN． 在△ACM 和△BAN 中,
+ ∠BCA = 180o ．

你能告诉我题目,我就能告诉你答案.
不要焦虑,把书上的问题一个一个找出对应的答案,理解其中的知识道理了,就会考出好成绩的.高一生物还是很多是常见的知识,就算平常学的不太好,也不要给自己压力,实在不行,划出重点,背下来.

=2013^2012*(-4)+2013^2012-2013^2012*3
=2013^2012*(-4)+2013^2012*(1-3)
=2013^2012*(-4-2)

是秋季学期+春季学期,就是上学期 下学期的意思,一般学校开学是在9分月,也就是秋季,另一个开学在3月,也就是春季.

我只知道这个题目的意思是2012-2012一个课程要记住.

一般这种试卷学校是不会外传的,只有你上家教老师那儿说不定会有!

1 2012-2013 学年七年级英语上学期期末考试试题 姓名 ———— 一、 单项选择：（每小题 1 分,共 15 分） ( )1. English is useful subject, and I do my English exercises( 练习 ) for hour every day. A. a; an B. an a C. a; / D./ an ( )2. ---Is ______ your uncle? --- No, ______ my father. A. him; he B. his; he's C. he's; his D. he; he's ( )3. Please call me ______63002371 ______ Monday morning. A. at, for B. at, on C. with, in D. on, of ( )4. My little sister Berry is ______ years old. Today is her ______ birthday. A. nine, nineth B. ninth, ninth C. nine, ninth D. ninth, nine ( )5. I like math __ ____ I don’t like math exams( 考试 ). A. and B. but C. or D. so ( )6. I like _____ and ___ . A. tomatoes , strawberrys B. tomatoes, strawberries C. tomatos, strawberries D. tomatos, strawberrys ( )7.. --- Let’s ____ ice -cream . ----- I don’t like ______, A have, it B. to have , them C. to eat ,it D. eat, them ( )8. Their mother _______apples very much. A. doesn’t like eat B. don’t like eating C. like eating D. likes eating ( )9. ____ Lucy your friend ? ___ she like bananas ? A ． Is , Is B. Does, Does C . Is ,Does D. Does , Is ( )10. The socks are ____ sale $ 2.5 . A. on for B. at; for C. on; at D. in at ( )11. What _____ Tom like _____ for lunch ? A. does ,eat B. is , eat C. does ,to eat D. is to eat ( )12. Jack is a ____ boy . He eats _____. A. good, good B. well, well C. good , well D. well, good ( )13. Thank you for . A. your help B. you helping C. helping me D. A or C ( ) 14When_____ you have a speech contest( 竞赛 )? --- Sorry, I______ know. A. are, don't B. do,aren't C. are,aren't D. do, don't ( )15. ---When ____your birthday? ---_________December 2nd. . A.is, lt's B.is, lt on C.are, They're D. does, O n 二、词汇 : 根据首字母和汉语提示填空：（每小题 1 分,共 10 分） 1.There are four ( 周 ) in a month. 2. She likes__________ （蔬菜） and fruit for breakfast. 3 We have many c lothes at very good p ． 4The socks are two （美元）． 5 Thursday is the f day of the week. 6. （来） and see for yourself. 7. The store s many school things. I often buy some from it . 8 ． --- What c ____ do you like? --- I like purple. 9. --- We have an English p tomorrow evening. --- Have a good time. 10. We have an art lesson for two h every week . 三、完形填空.（每小题 1 分,共 10 分） 请根据短文内容和语法,从 A 、 B 、 C 、 D 四个选项中选出最佳答案,并把答题卡上对 应题目的答案标号涂黑. Dear Jack, Thanks for your letter asking for a pen friend. I want to be your pen friend! Now let me tell you something about my life here in Chongqing, China. I am 1 English boy. My name is Jim Gross. I’m twelve. I have a Chinese name --- Gu Qingshan. I have 2 good friends at school. They are Li Lei and Han Meimei. Han Meimei is a Chinese 3 . She is eleven. She and I 4 in the same class, 5 Li Lei is not in my class. Miss Gao is 6 English teacher. Miss Chen is our Chinese teacher. Mr. Shen is our PE （体育） teacher. He likes us. He often 7 to the movies （看电影） with us. He 2014初中期末考试题库语文数学英语物理化学 2 doe sn’t like Beijing Opera because he thinks it is 8 . But he likes comedies （喜剧） , 9 they are exciting. He also likes scary thrillers （恐怖片） . I think our teachers are all good, so we 10 them very much. Please write soon! Best wishes! Yours Jim （） 1. A. an B. a C. the D. / （） 2. A. one B. two C. three D. four （） 3. A. boy B. brother C. sister D. girl （） 4. A. am B. is C. are D. do （） 5. A. and B. but C. or D. for （） 6. A. us B. our C. we D. their （） 7. A. plays B. sees C. goes D. likes （） 8. A. boring B. exciting C. interesting D. funny （） 9. A. but B. why C. then D. because （） 10. A. love B. have C. help D. play 四、 阅读理解.（每小题 2 分,共 40 分） 请阅读下列材料,并根据文章内容从 A 、 B 、 C 、 D 四个选项中选出最佳答案,并把答 题卡上对应题目的答案标号涂黑. A How does Emily spend a week? Monday Practice playing volleyball 3:00 p.m. -5:00p.m. Tuesday Go to see Mike in Children’s Hospital( 医院 ) 8:30p.m. — 10:30p.m. Wednesday Part-time job( 兼职工作 ) 1:00p.m.-5:00p.m. Thursday Go to the station( 车站 ) to meet her uncle Scott 9:00a.m. Friday See Mr. Green 10:30a.m. — 11:30a.m. Part-time job 2:00p.m. — 6:00p.m. Saturday A birthday party for Kate 7:00p.m. — 10:00p.m. Sunday Help Tony with his math （） 1. Where does Emily meet Scott? A. At Tony’s house. B. At Emily’s house. C. At the station. D. In the hospital （） 2. How many hours a week does Emily do her part-time job? A. Five hours. B. Eight hours. C. Ten hours. D. Eleven hours. （） 3. is ill( 生病 ) in hospital. A. Emily. B. Kate C. Mike. D. Scott （） 4. Her uncle Scott is coming( 来 ) on . A. Saturday B. Friday C. Thursday D. Wednesday （） 5. What does Emily do on Saturday evening? A. Have a birthday party. B. Study with Tony. C. Play volleyball. D. Do a part-time job. B 根据下面三则广告回答后面的问题.

1、小李想做一辆以空气为动力的玩具小车,他在做之前应考虑一些什么问题：
（ 车身材质要轻）、（减小车轮摩擦力）、（车身流线型）.
2、当一张纸和一个小球同时从同样的高度落下的时候会（小球先）落地,原因是（纸片受空气阻力比小球大）.把两张同样的纸,一张不变,另一张揉成团再做同样的实验会（纸团先）落地,原因是（纸片受空气阻力比纸团大）.

与尔（二）相识,一生（一三）相惜.
我大概是这个立意,楼主可以发挥你的文采,改一改.

B A B A A B B C C B B C B A B 错了别找我

第一题 用线性规划,分子分母同时除以x^2y 另y/x=t 然后画图
第二题 运用COSa在区间[-1,1]内
这两题上学期老师讲过的
我今天上学了,

一、选择题（共50分.1—20题,每题1分；21—35题,每题2分）
1-5 DCBAC； 6-10 AADDC； 11-15 CBCDC； 16-20 CBBAD； 21-25 DCCDD； 26-30 DACDD ； 31-35 DCBAC
二、填空与图示题.（本大题共3小题,共28分.）
36．（第6小题3分,其余每空1分,共14分.专业术语写错别字不给分.）
（1）神经和体液 ；
（2）B（A、B同时答也给分,只答A不给分）；皮肤血管；
（3）A；C；
（4）D；糖蛋白（或蛋白质）；④⑤⑧⑨⑩（答有③也对）(答到3个就给分,但答有错的不给分）；拮抗；
（5）降低 HCO3- （或 HCO3- , HPO42-）
（6）（画对一个箭头得1分,共3分）
37．（每空1分,共8分.专业术语写 错别字不给分.）
（1）f、Y（答全才给分）
（2）B细胞增殖、分化（形成浆细胞和记忆细胞）；体液；
（3）e；
（4）同种且生理状态相同的；一段时间后再接种等量同种病毒；④；k；
38．（每空2分,共6分.） （1）a；（2）c；(3)d
三、探究与实验题.（本大题共1小题,共22分.）
39．（每空2分,共22分.专业术语写错别字不给分.）
（1）（生物）群落；
（2）样方法；
（3）不同浓度的Cu在小麦不同生长发育时期对土壤线虫数量的影响；36
（4）①预实验；不能；设置浓度范围过小 (或未设置10-10——10-6NAA浓度的溶液进行实验,其实验结果不准确.其他合理答案也给分） ②浸泡法；沾蘸法；无关 ③形态学下端

曾经也和你一样 不过现在想到以前是多么的幼稚
好好学习 高二努力一把还能飞的高
一个过来人的劝告

2012+2012²-2013²
=2012×（1+2012）-2013²
=2012×2013-2013²
=2013×（2012-2013）
=2013×（-1）
=-2013
(*^__^* *^__^* *^__^*)你好,能够帮助你是我最大的快乐!如有疑问请追问,
如果您认可我的回答.请点击下面的【选为满意回答】按钮,谢谢!

http://wenku.baidu.com/view/1192862dccbff121dd368338.html

这个队在将要举行的比赛中胜x场，则要输（32-x）场，由题意得：
2x+（32-x）≥48，
故选：A．

28. B 我认为你不是故意的.mean to do打算做某事.
29. B be supposed to do,这是个省略句,状语从句的省略,省略主语和be啊.
30. B 这是个倒装句啊,主语是two villages,lie表示“位于”.
31. D convince sb of sth.
32. D 什么呀?恰恰相反,我很讨厌做饭呢.
33. B have sb do sth..sb就是英文词who.
34. B if从句用had+pp,助于用would have done.省略if倒桩,had提前啦.
35. A 没关系,多加练习,你会成功的.

每两个一组-1+2=1-3+4=1共有2012/2=1006,余一个-20131*1006-2003=-997

cdbbc,dcccb,cabac,c,相同 不相同 24 13 5 23 剩下的实验与大题网上有,自己搜能搜到

水平测试参考答案、1.C 2.C 3.C 4.B 5.A 6.B 7.A 8.C、9.x = - 7 10.10,等式的性质 211.- 2 12.5 13.4 14.4 15.2016.2（x - 1）+ 3x = 13、17.（1）x = -1；（2）x = 2.718.由题意,得 2 m + 5 + 2m -(1= 21.解得 m = 2.2)19.设火车长为 x米,根据题意,得x + 600=x.解得 x = 120.305所以,火车的长度为 120 米.、20.（1）不正确；①；（2）① 去分母时不能漏乘项；② 当括号外的因数是负数时,去括号后括号内的每一项都要改变符号.（3）去分母,得 3（x + 1）- 2（2 - 3x） = 6.去括号,得 3x + 3 - 4 + 6x = 6.移项,得 3x + 6x = 6 - 3 + 4.合并同类项,得 9x = 7.系数化为 1,得 x =7.921.设水流速度为 x千米 /时,根据题意,得 8（20 + x） = 12（20 - x）.解得 x = 4.则 8（20 + x） = 8 ×（20 + 4） = 192.所以,水流速度为 4 千米 /时,A、B 两码头之间的距离为 192 千米.选做题22.由题意,得 3（x + 2）- 2〔3（x + 2）- 2〕= 4.解得 x = - 2.所以使等式成立的 x的值为 - 2.23.设马驮了 x个包裹,则骡子驮了（x + 2）个包裹.根据题意,得 2（x - 1） = x + 2 + 1.解得 x = 5.则 x + 2 = 7.所以马驮了 5 个包裹,骡子驮了 7 个包裹.

作文题目：_______令我着了迷
课内：唯一的听众
科学我就不知道了
望采纳!

我不会因为我不知道是那份卷子,谢谢合作.

在用水平拉力作用于小球的过程中,水平拉力做的功使小球升高,转化成了小球的势能,
而小球升高的高度是L - Lcosθ = L(1 - cosθ)
所以, 水平拉力做的功是:W = mgL(1 - cosθ)
重力做功为 -mgL( 1 - cosθ)
因此,答案应选C

亲爱的一般这种问题没人有答案的 你应该把题目发上来