Elementary School Mathematics Lecture Draft of additive commutative law and the Law of Addition.

additive commutative law and the Law of Addition

Analysis of the textbook and learning situation

This lesson is the first lesson of Unit 7 of Book 7 of Primary School Mathematics published by Jiangsu Education Press. Incomplete inductive reasoning is adopted in the textbook, and students' favorite activities in life are arranged to jump rope and kick shuttlecock, so as to find out the number of participants. Then let the students compare, discuss, observe and discover the * * * similarities between different solutions, and thus deduce the additive commutative law and addition associative law. In practice, students are paid attention to the simple value of operation law. This arrangement not only cultivates students' enthusiasm for autonomous learning, but also enhances their awareness of applying mathematics. This lesson is the content of further exploration on the basis of addition calculation and checking calculation that students have learned, and it is also the basis for simple calculation in the future.

Talking about teaching objectives and teaching difficulties

According to the content of teaching materials and the requirements of new curriculum standards, students should use existing knowledge to construct new knowledge in cooperation and exchange, and formulate the following teaching objectives.

1. Through observation, comparison and analysis, the additive commutative law sum associative law is summarized.

2. In the process of learning, understand and master additive commutative law and the law of association, and perform operations.

3. Cultivate students' ability of analysis, judgment and reasoning, and improve their ability of solving problems.

According to the teaching objectives and students' ability to understand mathematical knowledge, the following points are made:

Teaching emphasis: to understand additive commutative law and the law of association, and to use it correctly.

Teaching difficulties: additive commutative law and the law of association are summarized through observation and analysis, and will be expressed by letters.

Speaking teaching method and learning method

Teaching mainly adopts guidance-inquiry, so that students can learn by guessing-verification

Speaking teaching procedure

First, the story is pregnant, and a new lesson is introduced

The story "chop and change" is recorded and played, so that students can talk about their thoughts after listening to this story, and (leading to the topic)

Story introduction can stimulate students' learning.

Show the book situation diagram and introduce

According to the information provided, put forward the problem of addition calculation.

Default:

1. How many people jump rope?

2. How many girls are there?

3. How many people are there between the boys who jump rope and the girls who kick shuttlecock?

4. How many people are there in the activity?

design intent: create a life situation close to students, and let students ask questions freely, which can cultivate students' divergent thinking. At the same time, the questions raised by students, as learning materials for subsequent inquiry, conform to the concept of "creative use of teaching materials" in the new curriculum.

third, guide the inquiry and construct the model.

(a), study additive commutative law

1, solve the problem, preliminary perception.

according to the question, "how many people participated in skipping rope?" Students' oral presentation. It leads to the conclusion that the two formulas have the same result and can be connected by an equal sign. Blackboard: 28+17 = 17+28

2. Arouse a guess and give an example to verify

Q: Is it true that all two numbers are added, the position of the exchange addend and the sum remain the same? Since it is a guess, it needs to be verified. How to verify it? (blackboard writing: conjecture verification)

Please give examples to verify the conjecture on the exercise paper. Students write equations. Then, the formula is exchanged, and the preliminary perception law is obtained. [+ _ xxJXSJ. =}

3. Observe the equation and find the law.

q: look at these equations and tell me what they have in common.

4. Guide students to explore additive commutative law's expression.

① The teacher asked: Can we use an equation to express the law we found? Discuss at the same table. Report:

Preset 1: We use numbers (words) to represent

2: We use symbols to represent

3: We use letters to represent

② Comparing different ways of representation, it is proposed that letters represent the law of discovery more concisely.

show the blackboard: a+b = b+a

point out that such a rule is additive commutative law. (writing on the blackboard)

Design intention: This link can closely focus on and use problem situations, and teachers and students can actively interact. Teachers can guide students to perceive the laws themselves, discover the laws, and learn to express them by letters. In the whole process, students perceive in observation, understand in imitation, and discover in exploration, which cultivates students' abstract inclusion ability.

(2) research on the law of additive combination

1. The theme map reappears

Research: How many people participated in the activity?

After the students make the formula, the equation on the blackboard is (28+17)+23=28+(17+23)

Observe and compare the above formulas, and think: What has changed on the left and right sides of the equation? What hasn't changed?

2. Enrich appearances and construct laws initially

Complete two sets of formulas in the book, and compare the "change" and "unchanged" on the left and right sides of the equation again.

q: what did you find?

3. Give examples to verify the rules.

Students cooperate in groups, and further give examples to verify the rules.

get the additive associative law, and try to express it in letters: blackboard writing (a+b)+c=a+(b+c)

Design intention: around the key point of "change and invariability", compare the two formulas in each group to get a preliminary feeling of the law. Then through students' personalized verification and communication, we can confirm the law of addition and learn to express it with formulas containing letters. In this way, the mathematical rational thought of "guessing, verifying and modeling" is infiltrated, and the students' ability of analysis, comparison, induction and generalization is developed.

(4), consolidate the exercise, expand and extend.

1. Complete the first question of "Think and do". Focus on the fourth is the use of exchange and association law together

2, complete the second question, focus on the students to talk about the benefits of combining the two numbers in the latter two questions.

3 to 1, who is faster.

38+76+24 (88+45)+12

4, 56+(14+7) = (□ +□) +□

(64 +□)+27 = 64+(□+27) < p How to calculate simply?

5. Game: Find friends.

(1) Which two students have leaves whose sum is 1?

(2) One classmate at the same table says a number, and another classmate immediately says a number whose sum with it is whole hundred or whole thousand.

design intent: several levels of practice provide students with valuable learning content, open their thinking space, improve their thinking content, compare students in observation and analysis, sublimate in thinking and comparison, and promote students to understand and master knowledge flexibly.

(5), the whole class summary, extended knowledge

What did we learn in this class today? How did you acquire this knowledge? So is there such a rule in subtraction, multiplication and division? You can continue to study after class.

summarize and consolidate the knowledge learned in time, and attach importance to the summary of learning methods. Make students consolidate the important and difficult points of this lesson again in their own summary. At the same time, it paves the way for students' future study;