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1、简单的三元一次方程组,前面所学的解二元一次方程组的基本思路及常见方法是什么呢？,基本思路:,代入消元法,加减消元法,那么如果解三元一次方程组呢？,1、了解三元一次方程组的定义； 2、掌握简单的三元一次方程组的解法； 3、通过解三元一次方程组进一步体会消元转化思想,小明手头有12张面额分别为1元、2元、5元的纸币，共计22元，其中1元的纸币的数量是2元纸币数量的4倍. 求1元、2元、5元纸币各多少张.,分析：,这个问题中包含有_个相等关系：,1元纸币张数2元纸币张数5元纸币张数12张,1元纸币的张数2元纸币的张数的4倍,1元的金额2元的金额5元的金额22元,三,设1元、2元、5元的纸币分别为x张
2、、y张、z张.,根据题意，可以得到下面三个方程：,x+y+z=12 x=4y x+2y+5z=22,观察方程、你能得出什么？,都含有三个未知数，并且含有未知数的项的次数都是1，像这样的方程叫做三元一次方程.,这个问题的解必须同时满足上面三个条件，因此，我们把这三个方程合在一起，写成,这个方程组含有三个未知数，每个方程中含未知数的项的次数都是1，并且一共有三个方程，像这样的方程组叫做三元一次方程组.,三元一次方程组中各方程的公共解叫做三元一次方程组的解.,那么如何求解这个三元一次方程组呢？,把分别代入消去x，得到关于y、z的二元一次方程组，解出y、z，然后再求出x.,例 解方程组,例题学习,解：
3、由得 z=x-4 ,所以，原方程组的解为,将分别代入，得,解这个二元一次方程组，得,把x=4代入得 z=0,解三元一次方程组的基本思路与解二元一次方程组的基本思路一样，即,三元一次方程组,消元,二元一次方程组,消元,一元一次方程,归纳,在解三元一次方程组时的消元与解二元一次方程组的消元有什么不同？解上面的方程组时，你能先消去未知数y（或x），从而得到方程组的解吗？,1. 解方程组：,2. 某校初中三个年级共有651人，八年级的学生比九年级的学生人数多10%，七年级的学生比八年级多5%，求三个年级各有多少学生？,解：由题意设七，八，九年级的学生人数分别为x, y, z人，得方程：,你解出来了吗？
4、,P22，A组第1题，B组第2题,1. 三元一次方程组的概念；,2. 三元一次方程组的解法；,三元一次方程组,消元,二元一次方程组,消元,一元一次方程,3.谈谈你对求解多元一次方程组的看法.,赠送：七年级英语 期末复习课,Unit 1A Trip to the Silk Road . 单词拼写 ()根据句意及首字母提示补全单词 1. He is friendly to everyone. I b_ he is a good boy. 2. Look! Wang Hong and Zhang Lin are walking a_ the river.,elieve,long,3. He is l
5、onely. Because he has f_ friends here. 4. English is one of the m_ subjects in our school. 5. When you c_ the road, please look left and right.,ew,ain,ross,()根据句意及汉语提示完成句子 1. The river is about four metres _(宽的). 2. John likes all kinds of _(乐器). 3. I am going to Beijing next week. Its a good _ (机会)
6、to try some Beijing Roast Duck.,wide,instruments,chance,4. My mother bought some new _(盘子) yesterday. 5. If you run too fast, you will _(跌倒) down. 6. My mother often keeps _(日记) in her free time. 7. Children need to know how to be _(安全).,dishes,fall,diary,safe,8. Class 8 is _(举行) a class meeting now
7、. 9. This summer holiday I went to the Hong Kong- Zhuhai-Macao _(桥梁) with my parents. 世纪 金榜导学号 10. The good news is very _(使人激动).,holding,Bridge,exciting,. 用方框中所给短语的适当形式填空 go for a walk, take a picture, take a tour, be famous as, a few 1. Zhang Jie _a singer. 2. There are _books in the bag.,is famou
8、s as,a few,3. Can you _of me before the tall building? 4. Mr Hu likes to _after supper. 5. Lets _during the coming holiday.,take a picture,go for a walk,take a tour,. 根据汉语意思完成句子 1. 我可以用一下你的词典吗? 当然可以。 _ I _ your dictionary? Sure.,May,use,2. 我校正计划和李明的学校一起环游中国。 My school is planning _ _ _ China _ Li Mi
9、ngs school. 3. 这是我校的通知。 _ _ _ _ _ my school.,a,trip,around,with,This,is,a,note,from,4. 我要给李明发一封电子邮件, 告诉他这个好消息。 I _ _ Li Ming _ _ and _ _ the good news. 导学号 5. 丝绸之路是由丝绸制成的吗? _ the Silk Road _ _ silk?,will,send,an,e-mail,tell,him,Is,made,of,6. 我们一起沿着丝绸之路旅行。 We _ _ the Silk Road together. 7. 从山海关到北京有多远
10、? 大约308千米。 _ _ is _ from Shanhaiguan to Beijing ? Its _ 308 _.,travel,along,How,far,it,about,kilometres,8. 我们没有足够的时间看到它的全部。 We dont have _ _ _ _ it all. 9. 在一个新地方你会玩得很开心。 You will _ _ _ _ _ in a new place.,enough,time,to,see,have,a,lot,of,fun,10. 这儿有一个标牌, 上面写着“禁止拍照! ” Here is a sign. It says “_ _! ”
11、 11. 成千上万只鸟住在这片森林中。 _ _ birds live in the forest. 12. 在回家的路上, 吉姆买了一个汉堡包。 _ _ _ _, Jim bought a hamburger.,No,photos,Thousands,of,On,the,way,home,Unit 2 Its Show Time! . 单词拼写 ()根据句意及首字母提示补全单词 1. The noodles t_ nice. Would you like some? 2. This computer is w_ 4, 000 yuan.,aste,orth,3. The Chinese i_
12、paper. 4. Im sorry I didnt r_ you are such a good teacher. 5. In a_ China, kings lived in the palaces. 6. The hamburgers are w_ food.,nvented,ealize,ncient,estern,()根据句意及汉语提示完成句子 1. He _(仍然) lives in a small house. 2. His _(旅程) to Tibet lasted for a week. 3. Could you _(描述) something about your scho
13、ol life?,still,journey,describe,4. We can get lots of _(经验) from our life. 5. This is my _(自己的) bedroom. 6. Her smile made me feel warm and lively. It was like a hidden _(财富).,experience,own,treasure,7. I have two sweaters. One is yellow and the _(其 他的) is red. 8. Mr Zhang gave us some good _(建议) on
14、 how to learn English well. 导学号 9. We _(应该) walk on the sidewalk. 10. Its raining hard. But he is _(还) standing on the playground.,other,suggestions,should,still,. 用方框中所给短语的适当形式填空 make a joke, work on, take part in, climb up , open ones eyes, talk about, place of interest, be famous as, think about
15、, have a rest 1. Mr Wang is _buying a new car.,thinking about,2. I will _an English competition next week. 3. How many _are there in your city? 导学号 4. Jim is good at _. 5. Lets _something interesting. 6. Hangzhou _a tourist city.,take part in,places of interest,making a joke,talk about,is famous as,7. Can you _the tree and pick an apple for me. 8. Youre tired. You must _ 9.
