Teaching content:
Jiangsu Education Publishing House's fourth-grade experimental textbook "Curriculum Standards" (Volume II), 106 ~ 107.
Teaching objectives:
1, let students experience the process of representing numbers by letters. Understand the meaning of formulas containing letters, find the value of simple algebra according to the value of letters, and master the shorthand method of algebra.
2. Make students experience the abstraction and generality of mathematics in learning activities, and feel the concise beauty and symbolic thinking of mathematics.
Teaching preparation: courseware, student's homework paper.
Teaching process:
Talk before class:
1. Enjoy the pictures related to the World Expo.
2. Talk about the meaning of the letters in the emblem.
3. Recall examples of things expressed by letters in life.
First, arouse life experience and reveal the topic.
1. Show the cards and talk about the values represented by A, J, Q and K.
2. Reveal the topic: These letters in playing cards represent several definite numbers respectively. Can letters represent changing numbers? Today, in this class, we will learn "number with letters" together.
Second, explore new knowledge:
1, create a situation, introduce a formula containing letters and express a simple relationship between quantity and quantity.
The courseware presents the scene of four little monkeys posing as triangles with sticks.
(1) displays 1 triangles made of sticks. Question: How many sticks does it take to make 1 triangle?
(2) Continue to show two, three and four triangles made of sticks in turn, and inspire students to express the number of sticks with the corresponding multiplication formula.
Follow-up: How many sticks does it take to put six triangles? 10?
(3) How did we calculate the total number of sticks just now? Guide students to summarize the quantitative relationship.
(4) Show the fifth monkey swinging a triangle, but the number of triangles can't be seen from the scene.
Thinking: the number of sticks used to put a triangle is:. (blackboard writing: a×3)
(5) What are the meanings of a, 3 and a×3 here?
(6) Do you know what number A stands for here?
Understand: A here can represent any natural number.
2, the game "guess the age", feeling that the formula containing letters can represent both numbers and quantitative relations.
(1) Quietly ask a student's age. On the blackboard: b, b+ 15. Q: Does B mean the age of the teacher? Or b+ 15 indicates the age of the teacher?
(2) Guide students to understand: From the formula b+ 15, we can see that the teacher is older than this student 15 years old.
(3) List the ages of students and teachers, and then ask: Can B here be 500?
Summary: Numbers expressed in letters have a certain range. The letter b stands for a changing number, but as long as b is determined, b+ 15 is also determined.
(4) Teacher: If the teacher's age is represented by n, how do you represent the classmates' age?
Teacher's summary: If the classmate is B, then the teacher is B+15; If the teacher is n years old, then this classmate is n- 15 years old. Here, b+ 15 and N- 15 can not only indicate the age of classmates, but also indicate the relationship between classmates' age and teachers.
3. Use letters to represent formulas and abbreviation rules.
(1) Review the calculation method of the perimeter and area of a square.
(2) Example 3. Can you use letters to express the formula of the perimeter and area of a square? (blackboard writing: C=a×4, S=a×a) Feel the simplicity of expressing the formula with letters.
Summary: Letters can not only represent specific numbers, but also represent quantitative relations, calculation formulas and so on. It is not only simple and universal, but also easy to remember and use.
4. Courseware demonstrates shorthand rules.
(1) Introduce shorthand rules with courseware.
(2) See the introduction of rules on page 106 of the textbook.
(3) Talk to your deskmate about the places that need our special attention in these rules.
(4) Emphasis: When the number is multiplied by the letter, the number should be written in front of the letter when the multiplication sign is omitted.
When 1 is multiplied by any letter, 1 can be omitted.
A2 stands for the product of two A's, pronounced as the square of A. ..
(5) With examples, further understand the shorthand rules and write on the blackboard.
Third, enjoy the "trip to the Mathematics Expo" and consolidate the practice.
1, the test of Haibao.
(1) "Think and do" problem 1: A simple way for students to write "x×x" after completing independently.
(2) judge right or wrong.
Emphasis: a×a means the product of two A's, which should be recorded as a2. It is explained on the blackboard that 2a=a×2=a+a, which means the addition of two A's, not only with different pronunciations, but also with different meanings.
2. Show the road map of the Mathematics Expo Park.
(1) Guide students to observe. What do the x meters and y meters in the picture mean respectively?
(2) The courseware shows that it takes meters to get there from the entrance. Students answer orally.
4. "Happy Life Museum", complete the fourth question "Thinking and Doing".
After the students finish independently, the whole class communicates and corrects mistakes.
5. Dynamic Concert Hall.
(1) Read the children's song Counting Toads.
(2) summarize children's songs with letters.
6. Introduce the mathematician Veda.