∴u(a∩b)=u{x|-2≤x≤3}={x|x<； -2 or x & gt3}.
Get the conclusion that U(A∩B)=(UA)∩(U B).
From graph (UA) ∩ (UB) = {x | x
Variant training
1. If the set U={ 1, 2, 3, 4, 5, 6, 7}, A={2, 4, 5, 7} and B={3, 4, 5}, then (UA)∩(UB) is equal to.
A.{ 1，6} B.{4，5}
C.{ 1，2，3，4，5，7} D
Answer: d
2. Let the set I = {x || x | < 3, x∈Z}, A={ 1, 2}, B={-2,-1, 2}, then A ∨( IB) is equal to ().
A.{ 1} B.{ 1，2} C.{2} D.{0， 1，2}
Answer: d
Example 2 let the complete set U={x|x≤20, x∈N, x is a prime number}, a ∩ (UB) = {3,5}, (UA) ∩B={7, 19}, (UA)∩.
Activity: Students review the meaning of set operation and make clear the elements in a complete set. The complete set U is represented by enumeration, and the elements in the set are filled into the corresponding venn diagram according to the conditions given in the question. The key to finding sets A and B is to determine their elements. Because the complete set is U, and the elements in sets A and B belong to the complete set U, because the set in this question is a finite set with fewer elements, it can be solved by venn diagram.
Solution: u = {2 2,3,5,7, 1 1, 13, 17, 19},
With the help of Venn diagram, as shown in Figure 8,
Figure 8
∴a={3,5, 1 1, 13},b={7, 1 1, 13, 19}.
Comments: This topic mainly examines the operation, venn diagram and reasoning ability of sets. With the help of venn diagram, this paper analyzes the operation problem of set, which makes the solution of the problem simple and vivid, and expresses the original abstract set problem intuitively, which embodies the superiority of the idea of combining numbers with shapes.
Variant training
1. Let I be a complete set, and M, N and P are all subsets of it, then the set indicated by the shaded part in Figure 9 is ().
Figure 9
∩[(IN)∩P]
B.M∩(N∪P)
C.[(IM)∩(IN)]∩P
D.m∩N ∩( N∩P)
Analysis: Idea 1: The shadow part is inside the set M, excluding C; The shaded part is not in the set n, excluding b and d.
Idea 2: The shaded part is in set M, that is, a subset of M, and the shaded part is in set N, that is, in ∩ p, so the set represented by the shaded part is m ∩ [(IN)∩P].
A: A.
2. Let U={ 1, 2, 3, 4, 5, 6, 7, 8, 9}, (UA) ∩B={3, 7}, (UB)∩A={2, 8}, (UA)∩.
Analysis: With the help of venn diagram, as shown in figure 10, the results of related operations are expressed, and sets A and B are naturally obtained.
Figure 10
Answer: {2,4,8,9} {3,4,7,9}
Knowledge and ability training
Exercise 4 in this section of the textbook.
Supplementary exercises
1. Let the complete set U=R, a = {x | 2x+1>; 0}, try to express the meaning of UA in written language.
Solution: a = {x | 2x+1>; 0}, namely the inequality 2x+1>; 0, and the elements in UA cannot make 2x+1>; 0 holds, that is, the elements in UA must satisfy 2x+ 1≤0. ∴UA is the solution set of inequality 2x+ 1≤0.
2. As shown in figure 1 1, where U is a complete set and M, P and S are three subsets of U, then the set represented by the shaded part is _ _ _ _ _ _ _ _.
Figure 1 1
Analysis: by observing the chart, we can see that the shadow part meets two conditions: first, it is not in the set S; The second is in the common part of the set m, p, so the set represented by the shaded part is the intersection of the complement of the set s and the set m, p, that is, (US)∩(M∩P).
Answer: (US)∩(M∩P)
3. Let sets A and B be subsets of U={ 1, 2,3,4}, and it is known that (UA)∩(UB)={2}, (UA)∩B={ 1}, then A is equal to ().
A.{ 1，2} B.{2，3} C.{3，4} D.{ 1，4}
Analysis: as shown in figure 12.
Figure 12
Because (UA)∩(UB)={2} and (UA)∩B={ 1}, there is UA={ 1, 2}. ∴A={3,4}.
Answer: c
4. Let the complete set U={ 1, 2, 3, 4, 5, 6, 7, 8}, set S={ 1, 3, 5}, T={3, 6}, then U(S∪T) is equal to ().
A.B.{2，4，7，8} C.{ 1，3，5，6} D.{2，4，6，8}
Analysis: directly observing (or drawing venn diagram) and getting S∪T={ 1, 3,5,6}, then U (S ∪ t) = {2,4,7,8}.
Answer: b
5. Given sets I={ 1, 2,3,4}, A={ 1} and B = {2,4}, then A ∨( IB) is equal to ().
A.{ 1} B.{ 1，3} C.{3} D.{ 1，2，3}
Analysis: ∫IB = {1, 3}, ∴a ∨( IB)= {1} ∨{ 1, 3} = {1, 3}.
Answer: b
Expand and promote
Question: There are 50 students in a class who solve two math problems, A and B. Of them, 34 are known to have solved problem A, 28 have solved problem B, and 20 have answered both questions correctly. Q:
(1) How many people answered at least one question correctly?
(2) How many people didn't answer these two questions correctly?
Analysis: First, the various types of solving two mathematical problems A and B are expressed by sets, and then their operations are written according to the meaning of the problems, and the problems are solved.
Solution: Let the complete set be U, A={ students who only solve problem A}, B={ students who only solve problem B} and C={ students who solve problems A and B at the same time}, then A∪C={ students who solve problem A}, B∪C={ students who solve problem B},
A∪B∪C={ Students who answered at least one question correctly}, U(A∪B∪C)={ Students who didn't answer both questions correctly}.
It is known that there are 34 people in A∪C and 20 people in C.
Therefore, it can be seen that A has 14 people; B∪C has 28 people and C has 20 people, so B has 8 people, so A∪B∪C has N 1= 14+8+20=42 (people), U (A ∪ B ∪.
42 people answered at least one of the questions correctly, and 8 people didn't answer both questions correctly.
Course summary
In this lesson, I learned:
① The concepts and solutions of complete sets and complementary sets.
② The complement operation of a set is often carried out with the help of the number axis or venn diagram.
homework
Textbook exercise1.1group A 9, 10, group B 4.
Design impression
The teaching design of this section pays attention to the thinking method of combining numbers and shapes, and in the teaching process, students should be guided to make up the set with the help of the number axis or venn diagram. Because the set in the college entrance examination is often closely combined with the inequality knowledge to be learned later, this section also reflects this point, so you can learn the knowledge of solving inequalities in your spare time.
Lesson preparation materials
Alternative example
Example 1 Given A={y|y=x2-4x+6, x∈R, y∈N}, B={y|y=-x2-2x+7, x∈R, y∈N}, find a.
Solution: y=x2-4x+6=(x-2)2+2≥2, A={y|y≥2, y∈N},
∫y =-x2-2x+7 =-(x+ 1)2+8≤8，∴B={y|y≤8，y∈N}。
So A∩B={y|2≤y≤8}={2, 3, 4, 5, 6, 7, 8}.
Example 2 let S={(x, y) | xy > 0}，T={(x，y)| x & gt； 0 and y & gt0}, and then ()
A.S∪T=S B.S∪T=TC。 S∩T=S D.S∩T=
Analysis: S={(x, y) | xy > 0}={(x，y)| x & gt； 0 and y>0, or x < 0 and y
A: A.
There are 1000 households in a town, of which 8 19 households have color TVs, 682 households have air conditioners, and 535 households have both color TVs and air conditioners, so at least one household has _ _ _ _ _ _ _.
Analysis: Let 1 0,000 households form a set U, including a color TV A and an air conditioner B, as shown in figure 13. There are 8 19-535 = 284 households with color TV sets and no air conditioning. There are 682-535= 147 households with air conditioning and no color TV, so at least one household is 284+ 147+535=966 households. Fill in 966.
Figure 13
Answer: 966
Knowledge expansion
Difference set and complement set
There are two sets A and B. If set C is a set of all elements belonging to A but not to B, then C is called the difference set of A and B, and it is recorded as A-B (or AB).
For example, A={a, b, c, d}, B={c, d, e, f}, C=A-B={a, b}.
It can also be represented by venn diagram, as shown in figure 14 (the shaded part represents the difference set).
Figure 14
Figure 15
In a special case, if the set B is a subset of the set I, and we regard I as a complete set, then the difference set I -B between I and B is called the complement set of B in I, and is recorded as B. 。
For example, I={ 1, 2,3,4,5}, B={ 1, 2,3}, b = I-b = {4,5}.
It can also be represented by venn diagram, as shown in figure 15 (the shaded part represents the complement set).
From the point of view of sets, the subtraction operation of non-negative integers is to know the cardinality of the union of two disjoint sets and one of them, and to find the cardinality of the other set, which can also be regarded as finding the cardinality of the difference set between set I and its subset B. 。
Instructional Design of "Basic Operation" Part III I. Objectives
By observing the paste activity, we find the elements in the intersection and difference of two sets, and try to place them according to the characteristics. Cultivate children's multi-latitude thinking ability.
Second, prepare
"Fruit Finding Home" and "Graphic Composition" are 1 slide (No.86-87), and each child has two exercise papers with the same content (see Exercise BookNo. 4-5).
Third, the process
(1) observation
1. Show fruit slides to guide children to think:
(1) What are the characteristics of the fruit in the left circle? (with leaves)
(2) What are the characteristics of the fruit where two circles intersect? (with leaves and stems)
(3) What are the characteristics of the fruit in the circle on the right? (pedicled)
(4) What are the two circles? How many are there in each?
2. Show a slide of graphics to guide children to think:
(1) What are the characteristics of things where two circles intersect? (Red, the number is 5)
(2) What are the characteristics of things in a perfect circle? (The number is five)
(3) What are the characteristics of the two circles? One for each person?
(4) What are the characteristics of the things in the left circle? (red)
(2) Distinguish
Let the children think: according to the characteristics, such as putting the fruit on the right or the baby face on the left into the circle, where should they be placed respectively?
Individual children dictate the location and reasons, as shown in figure (1). Peaches should be placed in the left circle instead of the right circle, because peaches have leaves and no stems. The round-faced doll in Figure (2) should be placed at the intersection of two circles, because she is red and the number of circles is five.
(3) Paste
Children will tear off the icons on the left (right) side of the exercise paper and stick them on the opposite positions of the two circles.
(Teachers tour to guide children to paste correctly)
Four. suggestion
(1) Physical materials can also be classified and placed in the collection and placement circle.
(2) The design of this activity can also be carried out twice.
Teaching design of "basic operation" 4 i. Teaching objectives
1. Make students learn to solve simple practical problems by intuitive and thinking set methods.
2. Through activities, students can master some basic strategies to solve overlapping problems and experience the diversity of problem-solving strategies.
3. Enrich students' understanding of intuition and develop thinking in images.
Second, the focus of teaching
Learn to use the meaning of intersection to solve simple practical problems.
Third, teaching difficulties
Feel the intersection with graphic method.
Fourth, the preparation of teaching AIDS.
Multimedia courseware.
Teaching process of verbs (abbreviation of verb)
(1) Brief introduction to life
1. Going to the cinema: Two mothers and two daughters went to the cinema together, but they only bought three tickets, and then they entered the cinema smoothly. Why? (Grandma, Mom, Daughter)
2. Xiaoming queues up: Xiaoming queues up to do exercises. Xiao Ming is the third from the bottom, the third from the bottom. How many children are there in this team?
The teacher guides the students: Can you explain it in your favorite way? Ask the students to draw pictures to explain.
The picture on the blackboard: ○● ○.
Students are smart and lively, active in thinking and like talking very much. The teacher is very happy to be friends with you. Today, we will have a math activity class-wide angle of mathematics.
(B) Review the past and learn new things.
1. The forest sports meeting is about to start. Let's take a look at the situation of small animals teaming up in basketball and football matches.
Show the Registration Form:
(1) Look at this table carefully. What mathematical information can you find? Talk to each other at the same table.
How many kinds of animals are there in the basketball game? What about those who take part in the football match?
(2) According to these mathematical information, what questions can be asked?
Student question: How many kinds of animals are there in the basketball match and the football match?
(3) Who can solve this problem: 17, 16, 15, 14.
There are several different answers now, so how many animals are there in basketball and football?
In order to solve this problem, we organized a painting competition. Draw your favorite pattern first, and write the animals participating in the basketball game and football game in the table. Note: how to write it so that everyone can see at a glance who is participating in the basketball game, which is participating in the football game and which is participating in both the basketball game and the football game? Let's see which group designed the chart which is both simple and scientific.
(1) teamwork, designed a variety of patterns.
(2) Students show their design works on stage, and the rest of the students are small judges.
(3) Put the displayed works together, which one do you like best and why?
The teacher also designed a pattern, will you also help the teacher evaluate it? courseware
(1) courseware presentation: basketball match and football match
(2) What do you think of the teacher's design?
(3) The teacher modified it according to your suggestion, and the courseware demonstrated the process of the intersection of two groups.
4. Look at the picture and answer first: What information does the picture tell you? courseware
(1) There are eight kinds of basketball players.
(2) There are nine kinds of football players.
Three kinds of animals take part in basketball and football matches.
(4) There are five kinds of basketball players.
(5) There are six kinds of people who only participate in football matches.
(6) There are 14 kinds of people who participate in basketball games and football games. Column expression: 8+9-3= 14 (species)
① Q: Why should we subtract 3?
Because these three kinds of participation, whether in basketball or football, are repetitive, they should be removed. )
(2) How to answer? Tell me what you think.
5+3+6= 14 (species)
(Five people only take part in the basketball game, six people only take part in the football game, and three people who take part in the basketball game and the football game at the same time solve the problem. )
9-3+8= 14 (type)
(9-3 means only taking part in the football game, plus 8 people taking part in the basketball game, you can also get the question. )
Teacher: This painting was created by a man named Wayne.
5. What are the advantages of comparing the set diagram with the table?
You can clearly see the repeated parts and other information from the figure.
(3) Consolidate exercises
1. Students like to use their brains and design their own solutions to problems. Using these mathematical thinking methods can solve many practical problems in life.
(1) Spring is coming and the sun is shining. There will be a sports meeting in the animal kingdom. Which animals will come to participate? Know them?
(2) Students talk about animal names.
The courseware shows the competition events: swimming and flying.
(3) What events can small animals participate in? Students discuss and give feedback.
(4) It turns out that these animals have so many skills. Come and sign up for the small animals. (Fill in the animal serial number in the textbook)
(5) Report: Tell me which animals can fly and take part in flying competitions, and which animals can swim and take part in swimming competitions. Students speak and demonstrate with animation.
When you visit swans and seagulls, talk about what activities they should take part in and why. Where should I put it? What does this mean in the middle of the intersection of two circles?
Animation demonstration: I can fly and swim.
2. Animation 6P 1 10-2 stationery store.
The students helped the small animals solve the problem of signing up for the sports meeting. Will you accept the challenge again?
(1) Courseware display: stationery store.
Courseware demonstration: Yesterday and Today of Stationery Wholesale.
(2) Looking at the picture, what do you find? Pens, rulers and exercise books are all wholesale these two days.
Yesterday's goods were (omitted), and today's goods were (omitted).
(3) How many kinds of goods are wholesale in two days?
Student formula: 5+5-3=75×2-3=75-3+5=7.
(4) Verifying the formula with animation.
The students went for a spring outing. There are 26 people with bread, 23 people with fruit, and 48 people with both bread and fruit. How many students are there in the spring outing?
(2) According to the line graph, students form:
26- 10+2323- 10+2626+23- 10
(3) What do you think?
4. Animation 1 1 (assembly drawing)
(1) Look at the picture to explain the meaning.
(2) Arrange students according to the materials provided by the animation.
Conclusion: When solving problems, we make good use of set circle or line segment diagram to help us analyze problems.
(4) Summary
What did you get from this lesson?
(5) Maneuvering exercises
There are 20 students in Grade Three, including math contest 15 and composition contest 13. (1) How many people participated in the math contest and the composition contest? (2) How many people only take part in the math contest? (3) How many people only participated in the composition contest?
"Basic Operation" Teaching Design Chapter 5 teaching material analysis:
Mathematics Wide Angle-Set is a textbook specially designed to introduce an important mathematical thinking method to students, that is, "Set". The textbook example 1 lists the students who participate in the Chinese group and the math group through statistical tables, but the total number is not the sum of the two groups, thus causing cognitive conflicts between students. At this time, the textbook intuitively expresses the relationship between the two extracurricular groups with a direct diagram (Wayne diagram), thus helping students find ways to solve problems. Textbooks only let students experience collective thoughts through subjects that are easy to understand in life, and lay the necessary foundation for subsequent study. As long as students can solve problems in their own way, they can.
? Teaching objectives:?
1. With the help of the direct view, students can initially experience the thinking method of set and perceive the making process of Wayne diagram.
2. Be able to use collective thinking to solve simple practical problems. ?
3. Students experience the value of mathematics in exploring and applying knowledge, and penetrate the consciousness of solving problems in various ways. ?
Teaching emphasis: with the help of intuition, let students experience the thinking method of set and perceive the making process of Wayne diagram.
Teaching emphasis: experience the generation process of set diagram and understand the meaning of set diagram, so that students can solve simple practical problems with the help of direct view diagram and set thinking method.
Teaching difficulties: experience the process of generating set diagram and understand the meaning of set diagram.
Teaching process:
First, the clever use of contrast, first of all to achieve "repetition."
1. Observe and compare (courseware has pictures) father and son
2. Question: There are two fathers and two sons. A * * *, how many people are there? How to calculate in the form of columns?
The first type: no repetition.
Huang Ming, his father Huang Weiguang. Li Yu, his father Li Wenhua.
Default: formula 1: 2+2=4 (person)
The second type: there is repetition.
Wang Cong, his father Wang Licheng, Wang Licheng's father Wang Huadong.
Equation 2: 2+2=4 (person) 4- 1=3 (person)
The teacher asked: Why did you subtract 1?
Second, the initial exploration, perceived overlap
1. Check the original data, resulting in duplication.
Teacher: Let's see that Class Three (1) is the lucky star chosen by the teacher. (Courseware demonstration)
calligraphy competition
Xiaoding
Li Fang
Xiao Ming
Ciovesson
Dongdong
Painting competition
Xiao Ming
Dongdong
Dandan
Zhang Hua
Wang Jun
Hong Liu
Teacher: What information have you learned from this form?
(2) Teacher: How many students took part in the competition?
Teacher: How can it be wrong? Take a closer look. Who can tell me?
(3) Teacher: How many people are there? Let's count.
What do you mean by repeating? Pointing to the second Xiaoming: "Does he count?" Why not?
(4) Teacher: Just now, you calculated that there were 1 1 people, and now we have only counted 9 people. 、
2. Reveal the topic. Title on the blackboard: overlapping problem.
Third, go through the process and build the model.
1. Stimulate desire and specify requirements.
Teacher: Just now, we carefully looked at the list of students in Class 3 (1) and found that two students repeated it, but can you tell which two people repeated it at one time from this list? It's hard, isn't it?
Teacher: It seems that my records are not clear enough. Let's do something. How can we redesign this list so that we can see it more clearly? Courseware display requirements: let people see clearly which five people participated in the calligraphy competition and which six people participated in the painting competition, and also let people see clearly which two people participated in both competitions. )
Please think about it. Do you have any ideas now? Before you say anything in a hurry, please show your thoughts on the exercise paper, ok? You can draw by yourself, and if you find it difficult, you can also cooperate with your classmates.
2. Explore independently and create venn diagram.
Students explore painting methods, teachers patrol, and find representative works to prepare for communication.
3. Show communication and feel venn diagram.
Teacher: I found that the students' painting methods are very creative. I chose some of them. Let's share them. We don't let the students who draw pictures introduce themselves, but let everyone see their paintings. I think this is a good way to make others understand without introducing yourself.
Default value:
The first case: marking.
Teacher: What do you think?
The second case: write it in front; Write it in front and circle it.
Teacher: What do you think? What are the advantages of this arrangement?
Teacher: (1) Who are the students participating in both events? Can you come up and point? We can circle them.
Guidance: Repeated students use two names, which is easy for us to misunderstand. If they use their names, they can also show that they participated in both the calligraphy competition and the painting competition.
The third case: students who participate in both projects are represented by one name (not written in the front).
Let me see: is it appropriate for him to write these two names here? Where should I write it?
The fourth case: it is represented by the previous name.
Teacher: What do you think? What are the advantages of this arrangement?
Teacher: What part of calligraphy is involved? Can you point it out? Do you want to circle it with a pen? How should the students who take part in the painting competition circle?
Teacher: What did you find when you turned around? Why?
Teacher: It seems that this adjustment can clearly show the repetitive and non-repetitive parts.
4. Organize painting and understand venn diagram.
(1) Dynamic demonstration of venn diagram generation process.
Teacher: Let the computer demonstrate the Wayne diagram created by our classmates again. Use a circle to represent the students who participated in the calligraphy competition, and then use a circle to represent the students who participated in the painting competition (the teacher drew two crossed ellipses in red and blue as he spoke) to demonstrate the formation process. Or two circles, the difference is that the two circles are not separated, but partially overlap. What can be represented only by this part where two circles overlap?
(2) Introduce the history of venn diagram.
Teacher: This kind of diagram was first put forward by the British mathematician Wayne, and later generations named it Wayne Diagram after him. The students are amazing. You and the great mathematician Wayne want to go together.
(3) Understand the meaning of each part of venn diagram.
(Courseware is presented in different colors to intuitively understand the meaning of each part)
Teacher: Look carefully. Do you know what each part of Wayne's chart means?
Teacher: A. What does the red circle mean?
B.what's in the blue circle?
C. what do you mean by two in the middle part?
D. What does the "purple part" on the left mean?
E. What does the "green part" on the right mean?
Teacher: Do you understand what each part of Wayne's chart means? Please talk to two classmates. (Students talk to each other)
(4) Highlight the advantages of venn diagram.
Let's compare this Wayne chart with the table just now. Which is better? Okay, where is it?
(5), the combination of number and shape, with venn diagram.
Teacher: Now, according to Wayne Tully's formula, can you find out how many people in Class Three (1) participated in these two competitions? Teachers patrol and find students with different methods to perform blackboard writing.
Default binding algorithm:
Health 1: 5+6-2 = 9 (person)
Health 2: 3+2+4 = 9 (person)
Health 3: 5-2+6 = 9 (person)
Health 4: 6-2+5 = 9 (person)
Look at the formula and ask questions: Look at the formula of the first student. Look at the picture and see the formula. What's your new inspiration? Teacher: Who asked him a question? (Health: Why subtract 2? (Courseware dynamic demonstration) Where is 5? Circle around. )
Focus on understanding why -2. Courseware dynamic demonstration
② Comparison:
3+2+4=9 (person)
5+6-2=9 (person)
A. There is a 2 in both formulas. What does this 2 mean?
Circles +2 and -2. Why is +2 in (1) and -2 in (2)?
B, can you find 5 in the first formula? 6?
What does c. 3+2 mean? What does 2+4 mean? This is the hidden information in the formula (1). Can you still find the hidden information in (2)? (Courseware demonstration)
Teacher: Now we can use so many methods to calculate that there are nine people in Class Three (1). Who helped us a lot? (Wayne diagram. )
Fourth, solve problems and use models.
1. Creating Situation and Life Application (Courseware Demonstration)
What can such a Wayne diagram represent in life besides the game just now?
Show life problems
(1) This is an overlapping problem in our science books. Did you find the overlap?
(2) This is an overlapping problem in our math book. Who is overlapping?
(3) This is a natural animal. Is there any overlap between them?
This is a feather duster. Did you find any overlap? Where is it? It seems that overlapping the wooden strips can increase the length and solve the problems in our lives!
(5) the problem of stationery stores.
Show me the following questions:
2. Solve problems with new knowledge.
Can you solve all these problems? (Finish exercise paper)
Feedback:
Question 1: (Life Question No.5) Can you express this information in Wayne diagram? Students fill in the Wayne diagram and figure out how many kinds of goods are imported.
Display: 5+5-3=7 (category)
2+3+2=7 (species)
Teacher: What does 3 mean here?
Why a +3 and a -3?
Teacher: Compare these two Wayne charts (the competition problem just now and the purchase problem now). What do they have in common?
Question 2: (Life Question 3 Animals in Nature) Compare right and wrong. The two children fill out different forms. Who do you agree with? Is there any good way to fill it in?
Question 3: (Life question 4: feather duster) How long is a * * *? What should we remind everyone?
Fifth, expand the variant and deepen the model.
Teacher: Let's go back and look at the school notice and the problem we solved: How many people should each class choose to participate in these two competitions? The answer we blurted out at first was 5+6= 1 1. Later, when I saw the entry list of three (1), I found that there were two duplicates, but actually there were only nine.
Let's think about this problem now. Class 3 (1)9 people. What about other classes? Class 3 (2), for example, must be nine people?
How many classmates may the teacher have sent? What are the possibilities? Can you draw a picture to show your guess?
Feedback: 5 people. Six people. Seven people. Eight people. Nine people.
Dynamic demonstration of courseware;
Teacher: What did you find after careful observation?
Students, such a problem that we thought was very simple at first, after our in-depth thinking, there is still so much knowledge.
Sixth, review and summarize and expand the model.
What did you learn from this course? What else do you want to know?