Teaching material analysis:
"Letters represent numbers" is the teaching content of the first lesson of solving equations on pages 85-87 of the fourth grade primary school mathematics textbook published by Beijing Normal University. This part is mainly to let students understand the necessity of using letters to represent numbers, experience the abstract generalization process of using letters to represent numbers, and learn to express simple quantities, quantitative relations and calculation formulas with formulas containing letters. This part is the basis for students to learn algebra knowledge in primary school, which can effectively cultivate students' abstract ability and generalization ability, help develop students' sense of symbols, and lay the foundation for students to learn the initial knowledge of equations in the future.
Teaching objectives:
Knowledge and skills
1. Understand the meaning of using letters to represent numbers under certain circumstances, and initially master the method of using letters to represent numbers, and can use formulas containing letters to represent quantities.
2. In the process of exploring the representation of numbers by letters, the model of letter formula is established, and the method, function and advantages of representing numbers by letters are fully realized.
3. Students can understand and master the method of expressing numbers, expressions and formulas by letters, and can solve related practical problems.
Process and method
In the process of learning, we can gradually feel symbolic thinking, develop students' sense of numbers and cultivate students' ability of abstract generalization.
Emotions and values
Let students gain successful experience in independent exploration, cooperation and exchange, and cultivate the spirit of unity and cooperation among students. Experience the concise beauty of mathematics and enhance students' mathematical emotion.
Teaching emphasis: understand the meaning of using letters to represent numbers and master the method of using letters to represent numbers.
Teaching difficulty: guiding students to experience the process of abstract generalization (that is, symbolization)
Teaching preparation: multimedia courseware? , onion video
Teaching process:
First, create a scene.
Students, the teacher met a difficult problem today. There is a nursery rhyme that I can't finish. Will you help me? (Show PPT theme map and children's songs)
Second, explore new knowledge.
1. Use letters to represent numbers.
Students read children's songs and count frogs. Teacher: Can you finish this nursery rhyme? Then can everyone try to finish the children's song in one sentence? Name answer: Health 1: How many frogs have several mouths. Student 2: There are countless frogs and mouths … Can you summarize this nursery rhyme in concise language? Discuss at the same table, (teacher's tour guide, say the numbers that can be expressed in letters appropriately). Roll call report: a frog A opened his mouth ... everyone is really amazing. A word can help me solve the problem. What do the letters here mean? Right: The letters here are all used to represent numbers. In this lesson, we will learn how to represent numbers with letters. (blackboard writing: numbers are represented by letters). So what does the front A mean (the number of frogs) and the back A mean (the number of frog mouths)? Is front A the same as back A? A letter represents the same number in the same question.
2. Use letters or formulas containing letters to express the relationship between quantities.
(1) Just now, everyone summed up the number of frogs and the number of mouths in a sentence by letters. Do you agree with these nursery rhymes after reading them? (PPT presentation). Let the students discuss before communicating: ① A frog has one leg (the number of frogs is different from the number of legs, so you can't use the same letter). A frog has two legs (you can't see that B is four times that of A). ③ Frogs have 4×a legs.
(2) Guiding analysis: What is the relationship between the number of frogs and the number of legs? Call the roll and answer: No matter what A means, 1 frog has four legs, which means that 1 4 frog has eight legs, which means that a 2×4 frog always has four times as many legs. If there is a frog with four legs, the formula is 4× A. Now who can sum up this nursery rhyme in one sentence? Answer by roll call: Frogs have four legs.
(3) Through the relationship between the number of frogs and the number of mouths and legs just discussed, can you express the following nursery rhymes in letters? (PPT) (Speak at the same table first and then call the roll). Emphasize the relationship between counting and the number of eyes and legs. (complete nursery rhymes. )
Finally, the teacher led the students to say: A frog, with a mouth, 2a eyes and 4a legs, plopped into the water.
Third, guess the age.
Play the onion video and calculate the age of dad's dog eggs. According to the students, Father Dog Egg is 30 years older than him. Can you calculate the age of dad's dog's egg? How old was the father 1 year-old? How old was the father of the dog egg when he was ten years old? ..... If a formula is used to express the age of the dog's egg father, how can we express the age of the dog's egg father? (a+30) What does A stand for in this formula with letters? What does a +30 mean? What number can A stand for? It seems that we often use letters to represent numbers in our lives. If a stands for the age of a dog's egg, what is the age of a dog's egg?
Into life
1. If milk powder is P yuan per bag and oranges are Q yuan per bag, it will cost () yuan to buy 10 bag of milk powder and 6 bags of oranges.
2. Teacher: P yuan per bag of milk powder, how to express 10 bag of milk powder; Q RMB per bag of oranges, how much is 6 bags of oranges? * * * How much? The teacher instructed the students to finish independently. Quantities are expressed in letters, followed by the sum and difference of units in parentheses.
3. Teacher: If you buy 1 kg of apples, it will cost () yuan per kg of m yuan. Let the students finish it independently, and then demonstrate it with courseware. Finally, emphasize: multiply the band score with the letter, turn the band score into a false score, and write it on the left side of the letter.
4.b cake is distributed to students A equally, so each student gets (). Let the students finish it independently, and then demonstrate it with courseware. Finally, it is emphasized that the division operation is written in fractional form. For example, B \a is usually written as b/a. ..
Try to practice.
1. Xiaoling's age is C. Her father is three times younger than her 1. Can you tell me her father's age?
The car travels from place A to place B at the speed of C kilometers per hour. After driving for 2 hours, drive 5 kilometers to reach the destination. Can you tell me the distance between A and B is () kilometers?
Let the students finish independently first, then report to the students, and finally give feedback to the results collectively, and then show them with courseware.
Fourth, consolidate practice.
1. The unit price of the exercise book is one yuan. How to express the total exercise book price of 100? (Total price of exercise books = quantity of exercise books x unit price) So 100 The total price of this exercise book is 100xa, that is, 100a.
The teacher emphasized that when a number is multiplied by the letter representing the number, the multiplication sign can be omitted or replaced by ".". Multiply a letter by a number. When omitting the multiplication sign, write the number before the letter. If ax 100 is written as 100a, it should not be written as a 100.
Four. Cooperative discussion
Let's review the examples we have learned. In these examples, letters represent numbers.
Specific requirements: 1. Write down the mathematical laws that your group wants to express in words. 2. This mathematical law is expressed by letters representing numbers. 3. Point out the meaning of each letter in this formula.
Teacher: Can you express the following mathematical laws in letters?
Additive commutative law: A+B = B+A.
Law of multiplicative association: (ab)c=a(bc)
Multiplication and distribution law: a(b+c)=ab+ac (let me talk about it first. Then use courseware to show)
Fifth, summarize the whole class.
Students, what have you gained through this lesson? It seems that through the study of this lesson, everyone thinks that it is very simple and convenient to use letters to represent numbers. Do you know who was the first person to use numbers in human history? Do you know how to show the courseware?
Seven, homework:
(1) What do letters mean in the following statements?
(1) It takes 10 to buy a shirt;
(2) The volume of a cuboid with a base area of 50㎝2 is 100b ㎝3.
(3) The teacher checked the homework of 20% students in the class, and there were 20% x copies.
(2) If Xiaoling's age is C and her father's age is 1 year younger than her, then her father's age is () years old.
Blackboard design:? Use letters to represent numbers.
A frog opened his mouth.
? 2× one eye 4× one leg 1 1+28
? Dog egg age (years old) Dad age (years old)
? 1+30
? 13+30
a+30
Teaching reflection: in this class, we try to teach onion micro-class. Students like it very much, and their attention is relatively concentrated, and their learning enthusiasm is very high. Moreover, the difficulties in the course are clearly decomposed by the onion video, which is easy for students to understand. There are problems in the video, which leaves room for students to think and discuss, and students' interest in learning is greatly improved. Because my teacher qualification certificate is mathematics, but because the school lacks Chinese teachers, I have always brought Chinese, and my preparation is not sufficient, which has not achieved the expected results. I hope Chinese also has such videos to help us, thank you! You have worked hard.