1, knowing the operation sequence of mixed operation with parentheses, will use parentheses to calculate off-type calculation problems, and will use abstract and generalized language to say the operation sequence; Gradually standardize the reading of formulas; Can use brackets reasonably according to specific problems, and deepen the understanding of the role of brackets.

2. Two-stage mixed operation with brackets is calculated by transfer analogy method. Through comparative observation, let students fully analyze and feel the role of brackets.

3. Develop the good habit of looking at the operation sequence before calculating; Cultivate good qualities of carefulness.

Emphasis and difficulty in teaching

Teaching emphasis: knowing the operation order of mixed operation with brackets will calculate the problem of unbalanced calculation with brackets.

Teaching difficulties: brackets can be used reasonably according to specific problems to deepen the understanding of the role of brackets.

teaching tool

courseware

teaching process

Talk before class: Do students like fruit? What kind of fruit do you like to eat? Baiguoyuan has all kinds of fruits. Let's go and have a look today.

First, create a situation and review the introduction.

Teacher: Do you know that sunny April is the season for strawberries to ripen? (Play the picture of picking strawberries quickly) Today, the uncles and aunts of Baiguoyuan want to invite everyone to pick strawberries together. Do you want to go?

Review (activity 1: picking strawberries)

Teacher: There are many strawberries in the strawberry garden. Can you pick them? If you want to pick strawberries, be sure to tell the operating sequence of each formula on strawberries. Do you have confidence?

(Statement requirements: Tell me the operation order of each of the following questions, what should I count first? What is it? )

3? 6? 2 5? 4+ 13 10-(5+3) ( 1) 10-(5+3)

Teacher: What's the first thing? What is it?

Health:

Teacher: Why do you have to count 5+3 first? reason

Health: There is a bracket in the box. You should count the brackets first.

Teacher evaluation

Summary: This is a parenthetical mixed operation sequence that we learned in the first grade. If there are brackets in it, count them first.

(2)7? 7-5

Teacher: Tell me about its operation sequence?

Health:

Two. Teaching the application of migration

Teacher: There are subtraction and multiplication in this problem. What if I want to subtract 7-5 first?

Health: put brackets.

Teacher: Where should I add it? (Call the students to demonstrate on the blackboard) Why do you put brackets?

Health: If there are brackets in the formula, count the brackets first.

Teacher: Oh, it turns out that he has mastered the brackets in the formula. First, he should calculate the rules in parentheses and understand the function of parentheses. You are really a clever boy. Let's applaud him!

1. Now add parentheses. Who will tell us about its operation sequence? What should I count first? What is it?

Health:

Teacher: In order to show the operation process of each step, will you take off the calculation? Please write down the calculation process of each step on the exercise paper. (tell the performance of the board of directors)

Feedback: Look at what this classmate wrote on the blackboard, right? 2 How did it come from? How did 14 come from? Oh, this student calculated 7-5=2 first, and then 7? 2= 14, did you write like him? Now please see the teacher write it again (generally speaking, the first step is at the back, and the previous numbers and symbols are also copied at the front). )

2. Reading method: We have calculated this formula, so can you read it? The default is 1: all students can read it. They just understand it as the difference between 7 and 5. what do you think? You read well (because the number calculated by subtracting 5 from 7 in brackets is called difference). Premise 2: Do they read the same thing, one right and one wrong? Which reading method is better? We must read the difference between brackets. Premise 3: All wrong. This reading is no different from the formula without brackets. Is it suitable? Listen to the teacher read it again: 7 times 7 MINUS 5; (Students and once) 3. Compare understanding

( 1)7? 7-5 and 7? (7-5) What's the difference between these two questions?

(2) The numbers are the same and the operation symbols are the same. Why are the calculation results different?

(3) The operation sequence is different? Whose reason is it? It seems that brackets are amazing, it can change the operation order of formulas!

Guide students to summarize and understand the operation order: if there are brackets in an expression, count them first.

4. Teacher, here is a formula with brackets. Do you understand? The blackboard shows: (77-42)? 7,

Teacher: Well, there are subtraction and division in this problem. Do you want to divide first? What should it be first?

Health:

Teacher: Oh, there are parentheses in the original formula, so you must count the parentheses first.

Who will tell you loudly, what is the problem first? What is it?

Off-die calculation in notebook. (tell the performance of the board of directors)

Feedback: Teachers and students complete the blackboard writing together.

5. Compare promotions:

(1) What are the similarities between these two questions?

Health: There are brackets.

Teacher: Like this, what should be calculated first when the formula with brackets contains two levels? (in brackets)

Teacher: Do you think the brackets are in the same position?

Student: Not the same.

Teacher: One is in the front and the other is in the back. Conclusion: You are really good at observing, but no matter where the brackets are, as long as there are brackets in the formula, we will.

Health: (Count the things in brackets first. ) teacher: you are really great!

Teacher: It seems that this parenthesis is really amazing. Let's read this amazing discovery aloud. (Teacher writes on the blackboard)

Blackboard writing: mixed operation with brackets

Third, practice practice:

1. (activity 2: fruit tasting)

How clever the students are. They not only picked strawberries successfully, but also found such important mathematical knowledge. It's amazing! Tell everyone a good news. An interesting fruit tasting party is being held in Baiguoyuan. Do you want to attend?

Please look at the requirements of the activity (what is the most important thing for each question? )

76? ( 12+25) ( 12? 5)? 3 48? (8? 2) (88? 56)? eight

Conclusion: These formulas all have the same feature, and they all have brackets. As long as there are parentheses in the formula, you should count the parentheses first. (72? 18)? 9 72? 18? 9 (1) What is the first question of this set of formulas?

(2) Are their calculation results the same? Let's go and have a look. Is it the same as you guessed?

(3) What caused their different results? (group discussion)

Health: parentheses, changing the order of operations, leading to different results.

Teacher: (77? 18)? Because there are brackets, you should count 77 first. 18, 35 again? 9; 77? 18? 9 If there are no brackets, do you want to count 18 first? Nine, then 77-2

Conclusion: This parenthesis is really amazing. If it is in the formula, you must calculate the brackets first. Furthermore, the operation sequence changes, resulting in different results. Since brackets have such a great function, can they be used well?

2.: (Activity 3: Picking apples)

I see some children may not have picked enough. How about the teacher taking everyone to pick apples?

Presentation requirements: fill in the blanks in the order of operation first, and then synthesize the formula.

(1) Answer the operation order of each graph.

(2) According to the operation order, the comprehensive formulas are listed independently.

feedback

Health: 43? 36? 2 1 2 1? 43? 36 2 1? (43? 36)

Teacher: Which of these three different arrangements do you agree to? Why?

Teacher evaluation

(3) Think about it: When do you need brackets and discuss it gently at the same table? (When the original operation sequence needs to be changed)

(4) Let's take a look at the instructions for the use of brackets:

In order to use parentheses as little as possible, mathematicians have stipulated the operation order:

If there is only addition, subtraction, multiplication and division in the formula, it should be calculated from left to right;

If there are both multiplication and division and addition and subtraction in the formula, multiply and divide first and then add and subtract;

Parentheses are only used when the order of the above two operations needs to be changed.

Fourth, talk about harvest.

Unconsciously, a pleasant class is coming to an end. Is everyone having a good time? What did you harvest in the beautiful orchard?

Write on the blackboard.

Parenthesized mixed operation

7? (7-5 ) (77-42)? seven

=7? 2 =35? seven

= 14 =5

If there are parentheses in the formula, count the parentheses first.