People's education printing plate fifth grade mathematics first volume teaching plan "using letters to represent numbers"

Teaching objectives of "using letters to represent numbers" (1)

Knowledge and skills: On the basis of old knowledge, students can further understand the operation rules and calculation formulas expressed by letters. Understand the meaning of the square of a number

Process and method: Make students express the operation rules and letter formulas in language, substitute numbers into letter formulas for calculation, and cultivate students' ability of abstract image and summary.

Emotion, attitude and values: Infiltrate letters into students to express the simple beauty of algorithms and formulas.

Emphasis and difficulty in teaching

Teaching emphasis: Arithmetic rules and formulas can be expressed in letters, and can be evaluated according to letter formulas.

Teaching difficulty: understanding the meaning of the square of a number.

teaching tool

Ppt courseware

teaching process

First, check the import.

1. Guide students to recall through exercises: What operation rules have we learned? And let the students describe the specific content of the corresponding algorithm in words.

2. Through the students' answers, the teachers sorted out: the learned algorithms are: additive commutative law, additive associative law, multiplicative commutative law, multiplicative associative law and multiplicative distributive law.

3. Complete the form according to the students' answers.

4. Teacher-guided thinking: How do you feel when you narrate?

It's very troublesome, sometimes I can't express myself clearly. )

Combine what you have learned and think about how to make it simple.

Students will think of using letters to represent numbers.

5. Expose the topic: So today we will continue to learn about using letters to represent numbers.

Second, the new interactive award.

(1) Teaching algorithms by letters.

1. Can you express these algorithms in letters like last time? (Show table of operation rules)

In order to unify teaching, students can be required to use letters A, B and C to represent numbers.

Think for yourself before you try to express yourself. Write the answers on the table on page 54 of the textbook. Collective revision.

Show the form completed according to the students' answers:

Additive commutative law a+b=b+a

Additive associative law (a+b)+c=a+(b+c)

Multiplicative commutative law ab=ba

Multiplicative associative law (a? b)？ c=a？ (b？ c)

Multiplication and distribution law (a+b)? c=a？ c+b？ c

2. Guide students to learn the abbreviation of multiplication independently.

Let the students read the textbook first, and then communicate and report.

Clear: in the formula containing letters, the multiplication sign in the middle of the letters can be written as? . ? , can also be omitted. Like a? b=b？ A can be written as a.b=b.a or ab=ba.

3. Guide observation and comparison: What is the difference between using words to describe and using letters to express the operation rules?

Let the students say it first, and then inspire them to sum up: it is clear at a glance, concise and easy to remember, and easy to apply to express the operation law with letters.

Question: What numbers can A, B and C stand for here?

Through communication, guide the students to understand that these three letters can represent any number we have learned.

(2) Teaching uses letters to express calculation formulas.

1. Show the shape of a square and ask: What is this? (square)

Let's talk about the formula for calculating the area and perimeter of a square: area = length? Side length; Perimeter = length? 4。

Guidance: The area and perimeter of a square can also be expressed by letters. General area is represented by S, perimeter is represented by C, and side length is represented by A ... Try to write a formula for calculating the perimeter and area of a square in letters.

Let the students try to write their own formulas in letters, and then turn to the books to see how the textbooks are expressed.

S= a？

C=4a

2. Question: Do you have any questions? Students may not understand the representation of squares.

Clear: S=a.a can be written as, a? Represents the multiplication of two a's, pronunciation? Square of a? So the formula of square area is generally written as S= a? .

Show: 3? ，b？ ,5? Let the students read the names and say what they mean.

(3? It is read as the square of 3, which means that two 3 times equals 9; b？ Pronounced as party b, it means two times b; 5? It is read as the square of five, which means that the multiplication of two fives equals 25. )

Let me see: a square with a side length of 6 cm. Can you calculate the area and perimeter of this square?

Guide the students to say the formula in letters first, and then calculate: the formula of square area is S=a? When a=6, S=6=? 6? 6=36 (square centimeter).

The formula for the circumference of a square is C=4a. When a=6, C=4? 6=24 (cm).

Third, consolidate and expand.

1. After reading page 56 of the textbook? Exercise twelve? Question 4.

Let the students analyze the information first? How many footballs were sold today? How to express it? (48+ m)

Then let the students calculate the second and third questions independently and correct them collectively.

2. After reading page 56 of the textbook? Exercise twelve? Question 6.

This question has two places that easily confuse students: A? 6? There are still 6? 2、a？ 2。 Teachers must guide students to distinguish correctly? Square? With what? Double? :a？ Represents the multiplication of two a's, which is a? a； 2a represents the addition of two A's, that is, A+A. ..

Fourth, class summary.

Teacher: What did you learn in this class? What did you get?

Guided induction:

The 1. algorithm is represented by letters, which is concise, easy to remember and easy to apply.

2. In the formula containing letters, the multiplication sign in the middle of the letters can be written as? . ? , can also be omitted.

3.a？ Read: the square of a means the multiplication of two n.

Homework: textbook page 56-57, question 12, question 5 10.

Blackboard design:

Use letters to represent algorithms and formulas.

Answer? b=b？ A can be written as a.b=b.a or ab=ba.

Answer? Read: the square of a means that two a's are multiplied.

Teaching plan of "using letters to represent numbers" (II) Teaching objectives

1 knowledge and skills:

[1] Let students understand and learn to use letters to represent numbers.

[2] Simple quantitative relations or calculation formulas can be expressed by formulas containing letters.

[3] Learn to find simple values with letter formulas.

[4] can use letters to solve problems

2 process and method:

[1] Let students experience the abstract process of expressing practical problems with formulas containing letters, experience the simplicity and convenience of letters representing numbers, and develop a sense of symbols.

3 Emotional attitudes and values:

[1] Let students realize the close relationship between mathematics and practical problems.

[2] Let students feel the rigor, generality and conciseness of expression.

Emphasis and difficulty in teaching

1 teaching points

[1] In order to understand the meaning of letters representing numbers, we will use formulas containing letters to represent numbers.

2 Teaching difficulties

[1] We can use the formula of meaning letters to represent numbers and realize the superiority of letters.

[2] can solve problems with letters.

teaching tool

Multimedia equipment

teaching process

Teaching process design

1 introduction

An activity

There are many good people and deeds in our campus. Look at a notice posted on the school bulletin board.

Lost?and?Found?

Today, students in Class 50 1 found a pink wallet with N yuan in it on the school playground.

Please ask the owner to claim it at the student office quickly.

201510 June 12

1. Student guess: How much money is there in the wallet? Can you write down its price?

2. What is the money in the lost and found office?

3. Ask students to discuss what specific numbers n can represent.

Today, in this class, we will learn to use letters to represent numbers.

(Title on the blackboard: using letters to represent numbers)

2 Explore new knowledge

1. Know how to represent numbers with letters or formulas containing letters.

(1) roll call: What's your name? How old are you?

Name and age of the blackboard student. (xxx 1 1 year) (as the case may be)

Teacher Dai is 20 years older than xxx. Do you know how old Miss Dai is this year? How to calculate? Think about it, when xxx 15 years old, how to calculate the age of Teacher Dai?

Think about it, how can Mr. Dai calculate his age below xxx? Publish and fill in the form:

(2) Highlight the contrast and realize the superiority of letters representing numbers.

Teacher: So, after writing so much, can you use a simple formula to express a teacher's age in any year?

Students try independently and remind them when necessary: If the letter A (blackboard A) is used to indicate xxx's age,

So how should the teacher's age be expressed?

Discuss and think, report and summarize

Blackboard: (a+20),

Do you think this is a good phenomenon? Tell me your reasons.

(3) Understand the specific meaning of letters representing numbers.

What does A stand for here? What does a+20 mean? Why can I use +20 to represent Miss Dai's age? By asking: What can A be? (Any natural number) Can A be equal to 200? Why?

Discuss the value of letters and guide students to understand the practical significance of mathematics in life.

(4) Learn to substitute the value of the formula.

When a= 12, do you calculate the teacher's age?

Tell me how you worked it out.

(5) Practice:

When a= 13, what is the age of the teacher?

a+20=( )+20=()

3 in-depth study

1, and the multiplication formula is expressed in letters.

(1) screen demonstration, posing as a triangle.

(2) Ask the question: 1 triangle, how many sticks do you need to put? (3) How many sticks does it take to put two triangles like this? 10? Please calculate it. How about an A?

2? 3=6 (root)

10? 3=30 (root)

(3) Inductive demonstration:

If a is used to represent the number of triangles, how do you represent the logarithm of the stick?

Why can you say that? (courseware demonstration: a? 3 )

(4) Pay attention to the specification of writing format: ① When a number is multiplied by a letter, can the multiplication sign be written as? Point? Or omit not to write;

② When a number is multiplied by a letter, the number is usually written in front of the letter.

Courseware demonstration: a? 3 = 3 amps

(5) Thirdly, deeply understand the specific meaning of letters indicating numbers.

What number can A stand for here? Can the A here be 200?

Why can't the A of a+20 be 200 when expressing age, and the A of 3 a here can be 200?

Guide students to know that letters have different meanings in different situations.

2. Letters represent algorithms.

(1) Teacher: What arithmetic rules have you learned so far?

Student: additive commutative law, additive associative law, multiplicative commutative law, multiplicative associative law, multiplicative distributive law.

Teacher: Then can you write additive commutative law as a letter?

Answer the teacher's blackboard: A+B = B+A.

Teacher: What are the advantages of this expression?

Health: concise, easy to understand, easy to remember and easy to use.

(2) Can you write down other algorithms?

Complete the table on page 54.

Courseware demonstration results.

Writing Tip: The multiplication sign in the middle of letters can be omitted, and other operation symbols cannot be omitted.

(3) practice: small judge. (Judge whether the following writing methods are correct)

Answer? 0.8 Write a0.8 () (When a number is multiplied by a letter, the number is usually written before the letter. )

5? 6 Write 56 () (When a number is multiplied by a number, the multiplication sign cannot be omitted. )

A+2 writes 2a () (When adding numbers, you can't omit the plus sign. )

Answer? B write ab () (when letters are multiplied by letters, the multiplication sign can also be omitted. )

3. Letter expression formula

(1) Teacher: What kind of figure is this? Do you know how to calculate its perimeter and area?

Health: Square area = side length × side length Square perimeter = side length ×4.

Teacher: If the side length of a orthomorphic shape is indicated by A, can letters be used to indicate its area and perimeter?

Students discuss and communicate.

Teacher's tip: the area can be represented by S, and the circumference can be represented by C.

Student report results: S = a X a C=4a.

Summary: S = a X a We can also write S = a2.

Reading: The square of A means the product of two A's.

Students read together.

(2) Practice:

1、

A = 3 cm

S = a 2 =( ) X ( )=( )CM2

Do you know what CM2 means?

C =4a=() X ()= () cm

2. Can you write the formula of the perimeter and area of a rectangle in letters?

S=()

C=()

4. Letters to solve practical problems

(1) courseware gives example 4.

A large glass of juice is1200g, and three small cups are poured. If the weight of each small cup is x grams, can you use a formula containing letters to indicate how many grams of juice are left in a large cup?

Students discuss and think.

Exchange report summary

Show courseware: What are the weights of three small cups? 3X Where's the rest? 1200-3X

Follow-up: What value can X be here? How about 500?

(2) Courseware example 5.

It takes three sticks to put a triangle and four sticks to put a square. How many sticks does it take to put X triangles and X squares?

Students discuss and think.

Show courseware: How many triangles are used? (3X) How many squares are used? (4 times)

How much did you use in that * * *? (3X+4X)

Can you make 3 times +4 times easier?

Students think, communicate and discuss.

Courseware presentation: 3X+4X=(3+4)X=7X.