First, the teaching content:
The content of this section is lesson 1, which is selected from pages 17 and 19 of the fourth grade mathematics textbook of People's Education Press.
Second, teaching material analysis:
On the basis of what students have learned about addition, this section clearly summarizes the meaning of addition, so that students can not only understand the meaning of addition, but also use addition to solve practical problems, and learn to further express by letters, laying a good foundation for learning "to express numbers by letters" in the future.
Third, the analysis of learning situation:
For primary school students, the generalization of the algorithm is abstract. Fortunately, students have learned some operation rules of addition and multiplication through the first phase of study, which is a favorable condition for this teaching. On this basis, this kind of teaching should focus on helping students to upgrade these scattered perceptual knowledge into rational knowledge.
Fourth, the teaching objectives:
1, combined with the specific situation, to know and understand additive commutative law and its significance.
2. additive commutative law can be abstracted, generalized and summarized, and can be expressed by a formula containing letters, and some simple operations can be performed by using additive commutative law.
3. Cultivate students' sense of symbols and their preliminary thinking ability of observing, comparing, abstracting and summarizing in the process of exploring laws, and stimulate students' interest in learning mathematics.
Five, the teaching focus:
Know and understand additive commutative law and its meaning, and express it with a formula containing letters.
Six, teaching difficulties:
Additive commutative law can conclude that additive commutative law can be used for some simple operations. Seven, teaching preparation:
PPT Courseware, Little Onion Class —— Symbolizing additive commutative law
Eight, the teaching process
1. Create a scenario and introduce a new course.
Listen to the story with questions (chop and change)
During the Warring States Period, there was an old man in Song State. He keeps many monkeys at home. One year, when the harvest was bad, the old man said to the monkey, "There is not enough food now, so we must save some food." How about eating three acorns every morning and four at night? The monkeys were very angry and said noisily, "Too few! Why didn't you eat more in the morning than at night? " The monkey keeper quickly said, "How about eating four in the morning and three at night?" The monkeys are all very happy.
Health: Laugh.
Teacher: Why are you laughing?
Health: Monkeys are so stupid that they eat the same amount of acorns every day.
Teacher: How do you prove it is the same?
Health: 3+4=7 (a) 4+3=7 (a) 3+4=4+3.
Teacher: Yes, the two ways of eating are different, so the total number of acorns eaten every day is the same. This is what we are going to study today: additive commutative law. (Blackboard: additive commutative law)
2. Show new lessons
Teacher: Students, do you like sports? How many students will learn to ride a bike? Cycling is a healthy exercise, isn't it? Uncle Li is traveling by bike! (The courseware shows an example of 1 scene.)
(1)) Get information and ask questions.
Teacher: Now please observe carefully. What does the tourist map tell us? What math problem do you want us to solve?
Health 1: Uncle Li rode 40km in the morning and 56km in the afternoon.
Health 2: The question is how many kilometers did Uncle Li ride today?
Teacher: Can you express the mathematical problem you want to solve with quantitative relation?
Health 1: distance by bike in the morning+distance by bike in the afternoon = distance by bike all day.
Health 2: The distance of cycling in the afternoon+the distance of cycling in the morning = the distance of cycling all day.
Teacher: Can you give me a detailed answer? Try it yourself. (Students' oral report)
(Teacher's blackboard) 40+56=96 (km)? 56+40=96 km
Teacher: The same travel map, the same question, we have listed two different formulas, both of which refer to adding up the distance of riding in the morning and the distance of riding in the afternoon, so the results of the two formulas are equal, which shows that what symbols can we use to connect the two formulas?
Health: Connect them into an equation with "=".
(Teacher's blackboard: 56+40=40+56)
Teacher: Please observe these two formulas carefully and tell me what you find.
Health: Add two numbers, exchange the positions of two addends, and the sum remains the same.
(2) Put forward a conjecture and verify it with an example.
Teacher: Does the formula of adding any two numbers have such characteristics?
Teacher: What kind of examples do you need to test the conjecture?
Health: Only by giving more examples and observing several groups of different formulas can we find the law.
Teacher: Can you name a few more such formulas?
(Students give examples to verify)
(3) Summarize the law and draw a conclusion.
Teacher: Although we write different equations, if we look closely, they contain the same laws. Did you find them? Can you talk about the law of discovery in your own words?
Students dictate, and the teacher immediately writes on the blackboard: Add two numbers, exchange the addend position, and keep the sum unchanged. This is called additive commutative law. )
Teacher: The students summed up this rule by observing the formula. Students are really amazing!
Division; Now that we have found the pattern, let's put a little video and let's get math information together (Little Onion Class-Symbolized additive commutative law).
Teachers and students: additive commutative law's alphabet expression. a+b=b+a
3. Apply what you have learned:
1. Fill in the appropriate numbers in the brackets.
766+589=589+( ) 300+600=(? )+(? )
□+=+( ) ? ()+( )=b+a
a+ 15=( )+()？ ( )+65=( )+35
2. Fill in the appropriate numbers in the brackets.
25+49+75=( )+( )+( )
4, class summary:
Today, we learned about additive commutative law, that is, adding two numbers, exchanging the positions of addends, and keeping and keeping the same. This is called additive commutative law. Expressed in letters as a+b = b+a.
5, homework layout:
Memory additive commutative law; Complete questions 2 and 3 in Exercise 5.
Nine, teaching reflection:
The new knowledge in this class has a corresponding cognitive basis in previous mathematics learning. Learning the new knowledge in this class can promote students to have a deeper understanding of the original knowledge and methods. In the teaching process of addition algorithm, I have always been student-oriented, grasped the law of students' understanding according to their age characteristics, and achieved good teaching results.