Teaching objective: 1. Through review, students can deepen their understanding of the laws and properties of operations, and can skillfully use them to perform some simple operations.
2. Experience the whole process of review, learn the methods of review, and improve the application consciousness of mathematics learning.
3. Cultivate students' awareness and ability to choose algorithms flexibly according to specific conditions, and develop students' flexibility of thinking.
4. Let students feel the connection between mathematics and real life, and use what they have learned to solve simple practical problems.
Teaching emphasis: using arithmetic and simple qualitative calculation.
Teaching difficulties: flexible calculation according to the characteristics of the formula.
Teaching preparation: PPT courseware, answer sheet.
Teaching process:
First, dialogue import
Students, we have finished learning three units of mathematics this semester. What are their contents? Please recall. (Four operations, position and direction, algorithm and simple calculation)
Which of these three units has the most content and the most difficulty? The students feel the same as me. Shall we use this lesson to sort out and review Unit 3 today? (Good) Title on the blackboard: Unit 3 Arrangement and Review
Second, sort out memories and build a network.
1. To review this unit well, please think about the topic map of this unit first. Uncle Li travels by bike, and his classmates plant trees on the hillside ...
What knowledge have we learned by using these thematic maps? Please talk to each other at the same table, and then tell the teacher by posture.
2. Report, communicate and organize knowledge points
(1) The algorithm of addition (additive commutative law, the law of additive association). Say it out, and then display the algorithm and the corresponding letter formula on the big screen.
A, the two addends exchange positions, and the sum is unchanged. This is called additive commutative law.
Expressed in letters: a+b = b+a.
B, add the first two numbers, or add the last two numbers and keep the same. This is the so-called law of additive association.
Expressed in letters: (A+B)+C = A+(B+C)
(2) The arithmetic rules of multiplication (multiplication commutative law, multiplication associative law, multiplication distributive law).
The first two can guide students to say it, and we should emphasize multiplication and division. The forms of multiplication and addition must be mastered, and the forms of multiplication and subtraction require top students to pass the exam. Then instruct the students to do two exercises orally, emphasizing that the algorithm can be used not only backwards, but also backwards.
First, exchange the positions of two factors, and the product remains unchanged. This is called the multiplicative commutative law.
Expressed in letters: a×b = b×a a.
B, multiply the first two numbers, or multiply the last two numbers first, and the product remains unchanged. This is the so-called law of multiplication and association.
Expressed in letters: (a× b )× c = a× (b× c)
C. When the sum of two numbers is multiplied by a number, you can multiply it first and then add it. This is the so-called law of multiplication and division.
Expressed by letters: (a+b) × c = a× c+b× c or: a× (b+c) = a× b+a× c.
Expand: (a-b) × c = a× c-b× c or: a× (b-c) = a× b-a× c.
Instruct students to answer the following two questions orally:
Simple calculation:
67 x 76 + 76 x 33 88 x 102
=76 x(67 +33 ) = 88( 100 + 2)
= 76 x 100 = 88x 100+88 x2
=7600 = 8800+ 176
= 8976
(3) The nature of continuous reduction.
A, a number minus two numbers in a row, you can use this number to subtract the sum of these two numbers.
Expressed in letters: A-B-C = A-(B+C)
B, a number subtracts two numbers continuously, you can use this number to subtract the last number and then subtract the previous number.
Expressed in letters: A-B a-b-c = a-c-b C-B.
(4) the nature of division.
A. A number is continuously divided by two numbers, and this number can be divided by the product of these two divisors.
Expressed in letters: a ÷ b ÷ c= a ÷ (b× c)
B, a number is divided by two consecutive numbers, you can use this number to divide the last number and then divide the previous number.
Expressed in letters: a \b \c = a \c \b c \b
The nature of the operation requires students to speak out, and the teacher gives appropriate hints. It is emphasized that each attribute can be reversed.
(5) Organization unit knowledge network diagram.
1. Teacher: Please fill in the relevant information in letters on the knowledge network diagram of this unit. Teachers patrol and guide poor students.
2. After completing the form, check with each other at the same table and ask the students to answer the law or nature respectively, and announce the correct answer on the big screen. Encourage students who do well in time, and remind them again that the operation law of multiplication is easy to make mistakes. (6) Four steps of inductive problem solving: (While inductive, write on the blackboard: look, think, calculate and check. )
A. (look) at the characteristics of data and operation symbols;
B. (think) what algorithm or nature do you want to use;
C. (calculation) clever calculation; D. (check) check.
Tips: When doing problems, you should consciously use simple methods to calculate, so as to improve the efficiency of doing problems!
2. Knowledge application and capacity development
(1) I will choose
Show multiple-choice questions on the big screen to guide students to understand the meaning of the questions and answer the first question. The second question allows students to choose freely after reviewing the questions, and the third question attracts students to find the correct answer after reading the questions. )
(1) 40× (8+25) = 40× 8+40× 25, in which () is used, which makes the calculation simple.
A. Multiplicative commutative law B. Multiplicative associative law C. Multiplicative distributive law
(2) 61+72+39+28 = (61+39)+(72+28) Use ().
A. additive commutative law B. Additive associative law C. additive commutative law and additive associative law
(3) 140÷ (5×7)=( )
A. 140÷ 5×7
(2) judge and correct.
Judgment: Correct what is wrong in □ in □.
Intention: Under the guidance of the teacher, understand the meaning of the question, announce the answers one by one, and emphasize the flexible application of the operation law.
(3) Solving problems
(4) Exercise: Calculate the following questions in a simple way.
( 1)85+ 126+ 15+74(2)25 x32 x 125(3)487- 139-87-6 1
(4)83x 47+53x 83(5)3600(36x 4)
Third, the teacher summarizes the dialogue.
Q: What did we review together in this class?
The laws of addition, multiplication, continuous subtraction and continuous division, as well as the flexible application of these laws and properties in specific topics, problem-solving methods and so on.
The students gained a lot today. Teachers sincerely hope that students should not only remember these laws and properties, but also learn to use them flexibly to help us solve practical problems in life, improve work efficiency and make our study easier and easier!