Knowledge and skills: Through scenario creation, students can make full use of their existing knowledge and experience to transfer knowledge in the process of solving practical problems. Under the guidance of the teacher, students explore and summarize the multiplicative commutative law and associative law, understand the functions of multiplicative commutative law and associative law, and understand that some simple operations can be carried out by using the algorithm.

Process and method: Encourage students to make bold guesses and learn the methods of scientific verification. Feel the connection between mathematics and real life, and use what you have learned to solve simple practical problems. Cultivate the consciousness and ability to choose the appropriate algorithm according to the specific situation and develop the flexibility of thinking.

Emotion, attitude and values: through creating teaching scenes and appreciating the beauty of natural scenery, students are infiltrated with environmental education.

Emphasis and difficulty in teaching

Teaching focus

Explore and discover multiplication, commutative law and associative law, and know how to use what you have learned to make simple calculations.

Teaching difficulties

Application of the law of multiplication and distribution.

teaching tool

multimedia courseware

teaching process

First, check the import.

Second, learn multiplicative commutative law and multiplicative associative law.

1. Learn Example 5.

(1) Example 5

(2) Students solve problems independently in exercise books.

(3) Guide students to report the problems solved.

4? 25= 100 (person)

25? 4= 100 (person)

What are the characteristics of the two formulas?

Can you give other similar examples?

The teacher writes on the blackboard according to the students' examples.

Can you give this law of multiplication a name?

Blackboard: Swap the positions of two factors, and the product remains the same. This is the so-called multiplication commutative law.

Can you try using letters?

The student report letter indicates: a? b=b？ a

2. Study Example 6.

(1) Example 6

(2) Students solve problems independently in exercise books.

Teachers patrol and give timely guidance.

(25? 5)? 2 25? (5? 2)

= 125? 2 = 10? 25

=250 (barrel) =250 (barrel)

(3) Guide students to report the problems solved.

What are the characteristics of the two formulas?

Can you give other similar examples?

The teacher writes on the blackboard according to the students' examples.

Can you give this law of multiplication a name?

Blackboard writing: multiply the first two numbers first, or multiply the last two numbers first, and the product remains the same. This is the so-called law of multiplication and association.

Can you try using letters?

The student report letter indicates: (a? b)？ c=a？ (b？ c)

(4) Complete the first question in Example 6.

3. Study Example 7.

(1) Example 7.

(2) Students solve problems independently in exercise books.

Teachers patrol and give timely guidance.

(3) Guide students to report the problems solved.

What are the characteristics of the two formulas?

Can you give other similar examples?

The teacher writes on the blackboard according to the students' examples.

Can you give this law of multiplication a name?

Blackboard: the sum of two numbers multiplied by one number. You can multiply them by this number first and then add them up. This is the so-called law of multiplication and division.

Can you try using letters?

The student report letter indicates: (a+b)? c=a？ c+b？ c

Answer? (b+c)=a？ b+a？ c

(4) Complete the first question in Example 7.

3. Study Example 8.

(1) Example 8.

(2) Collect information and define conditions.

(3) Students think independently and try to solve problems.

(4) Understand the process and implement different methods.

Summary after class

What did you buy today?

homework

1. Use the multiplication law and fill in the appropriate numbers on the horizontal line below.

78? 85? 17=78? (_____? ______)

8 1? (43? 32)=(_____? ______)? 32

(28+25)? 4= ? 4+ ? four

15? 24+ 12? 15= ? ( + )

6? 47+6? 53= ? ( + )

( 13+ )? 10= ? 10+7?

2. Judge right or wrong.

( 1)39? 22-39? 2=39? 22-2 ( )

(2)39? 22-39? 2=39? (22-2) ( )

(3)39? 28+39? 72=39? 28+72 ( )

(4)39? 28+39? 72=39? (28+72) ( )

(5)39? 12=39? ( 12-2) ( )

(6)39? 12=39? ( 10+2) ( )

Write on the blackboard.

Swap the positions of two factors, and the product remains the same. This is the so-called multiplication commutative law.

Multiply the first two numbers first, or multiply the last two numbers first, and the product remains the same. This is the so-called multiplicative associative law.

Teaching plan of multiplication law (2) teaching objectives

Knowledge goal: observe, compare, abstract and summarize the laws of multiplication and distribution through the exchange of old and new knowledge; Understand and master its structural characteristics; Understand and use multiplication, division and distribution methods for simple calculation, and can calculate correctly.

Ability goal: the method of understanding things from special to general, and then from general to special.

Cultivate students' ability of observation, comparison, abstraction and generalization.

Cultivate students' sense of numbers and symbols.

Emotional goal: let the children generate it themselves? A method of recording and sorting with symbols? Experience the joy of learning.

Emphasis and difficulty in teaching

Teaching emphasis: guide students to summarize the law of multiplication and distribution through observation, comparison and abstraction.

Teaching difficulty: applying multiplication and division to solve practical problems.

teaching tool

courseware

teaching process

(A) the introduction of life, perception of the law

1. Who do you like best at home? I also made a survey. Many students in our class are parents who get up early to prepare breakfast for you, send you to school and help you with your homework.

Mom and dad are so kind to us that we can proudly say? Do mom and dad love me? .

3. My parents love me. How can I say this sentence?

I heard that Zhang Lei and Yang Jun are new friends. What else can I say?

5. Summary: The same sentence can be expressed in different ways. What is this phenomenon in life in our mathematics? Today we will explore the laws in mathematics together.

[Strategy] Attach mathematical knowledge to common real-life problems, guide students to develop their spirituality, seek the essential connection between mathematical knowledge and real-life problems, and then handle relevant information reasonably, and combine vivid mathematical materials to touch students' moral collision, inject humanistic blood into the original single and indifferent content, and promote students' perception and internalization.

(B) open inquiry, legal construction

1. Introduction

At the beginning of this semester, the school will replace the desks and chairs for the first, second and third grades:

(Play the courseware), ask questions and make students think:

(1) Please observe the big screen carefully:

How much does it cost for the school to replace three sets of desks and chairs for the first grade?

How much does it cost for the school to replace five sets of desks and chairs for the second grade?

How much does it cost for the school to replace 6 sets of tables and chairs for the third grade?

(2) Ask two students at the same table to choose a question and answer it in two ways on the exercise paper?

(3) Tell me about your problem-solving method? What does your formula mean? What about the other method? Explain.

(4) Who wants to report it?

2. First discovery

(1) Look at these three formulas carefully. Can you find anything? You can discuss with your deskmate.

Summary: The results of each formula are equal.

(2) Can I connect these two formulas with an equal sign? Why?

Blackboard: (50+60)? 3 = 50? 3+60? three

(75+68)? 5 = 75? 5+68? five

(80+65)? 6 = 80? 6+65? six

3. The second discovery

(1) Look at these three sets of formulas again. Have you found anything else?

(2) Students, is your discovery just a coincidence or a guess? Can you give some such examples to verify your guess?

(3) Each person gives an example and writes it on paper, and then asks the deskmate to help verify it.

Reporting and Communication: Can you give some examples of this? Can you lift it?

4. Summary:

(1) The rule you find is called multiplication and division. What is deskmate multiplication and division?

(2) Please look at the big screen. Is that what you mean? Read quietly.

(3) Are there any words you don't understand?

5. Personalized understanding

(1) Can these equations be expressed in a preferred form? For example, use letters, graphics, etc.

According to the students' answers to the teacher's blackboard:

(□+○)? ☆=□? ☆+○? ☆

(A+B)？ C = A？ C+B？ The third/third in ten days' work

(a+b)？ c=a？ c+b？ c

(2) What do these equations mean? (Discuss at the same table and then report)

(3) How do you feel about the multiplication and distribution law expressed by letters?

[Strategy] In view of numerous mathematical facts, we should not rush to guide students to discover laws, but let students summarize the * * * characteristics of these equations in simple language. Are these characteristics? Multiplication and distribution law? The germination of knowledge is a gradual step for students to construct knowledge. On this basis, the law is derived and naturally comes. In particular, let students express their understanding of multiplication and division in a personalized way, which effectively promotes students' personalized perception of the meaning of the law.

(3) Activate contact and apply rules.

1. Please connect two equal formulas.

(8+ 13)? 4 4 1? (3+27)

3? (2 1+6) 7? 5 +8

4 1? 3 +4 1? 27 3? 2 1 +3? six

7? (5+8) 8? 4 + 13? four

Why is the connection so fast? Does it count?

(2) Why are these two formulas not related? Can it be explained by the content of multiplication and distribution law?

2. Fill in the blanks according to the law of multiplication and distribution:

(83+ 17)? 3=□? □○□? □

10? 25+4? 25=(□○□)? □

(1) Who wants to show what you filled in? Do you have any different opinions?

(2) Comparing the converted formula with the original formula, which one makes us feel easier to calculate? Why?

(3) Summary: After learning the multiplication and division method, you can choose the algorithm flexibly and calculate it simply.

[strategy] various exercises are also a kind of information source, and the process of solving problems is actually a kind of deepening understanding and accumulation? Energy? The process of learning is a process in which students broaden their knowledge horizons, improve their cognitive structure, enhance their cognitive realm and increase their wisdom in life.

3. Contact the old knowledge and establish contact with the existing knowledge.

Dialogue:? Multiplication and distribution law? Have you used it in your past studies? Let's review it.

Now I practice multiplication and vertical calculation every day and watch the big screen. Multiplication distribution law is also used in vertical multiplication? Did you get a look at him?

[Strategy] Guide students to connect the application of knowledge, arouse students' memory of existing knowledge, and grasp the wide application of multiplication table with the feeling obtained by personal calculation.

(4) class summary:

Today, you learned the laws of multiplication and distribution. what do you think?

(5) Blackboard design:

Powder companion

(50+60)? 3 = 50? 3+60? three

(75+68)? 5 = 75? 5+68? five

(80+65)? 6 = 80? 6+65? six

(a+b)？ c = a？ c+b？ c