Seventh grade rational number addition teaching plan I. Teaching objectives
1. Knowledge and skills
(1) Through the goal difference in football match, let students master the rational number addition rule and use it to calculate;
(2) In the teaching process of rational number addition rule, pay attention to cultivating students' computing ability.
2. Mathematical thinking
Through observation, comparison and induction, the rational number addition rule is obtained.
solve problems
Can use rational number addition rule to solve practical problems.
4. Emotions and attitudes
It is recognized that through the cooperation and communication between teachers and students, students actively participate in exploration and acquire mathematical knowledge, thus improving their enthusiasm for learning mathematics.
be concentrated
It can be operated by rational number addition rule.
6. Difficulties
The law of adding two numbers with different signs.
Two. Textbook analysis
? Rational number addition? It is the third section of rational numbers in the first chapter of the seventh grade mathematics book published by People's Education Press. There are four classes in this class, and this class is the first class. The design of this lesson is mainly to illustrate the significance of rational number addition and introduce the law of rational number addition through the example of goal difference in ball games for future study? Rational number subtraction? Lay a good foundation.
Three. Analysis of the situation of schools and students
Chongpo Middle School is a complete middle school in Guoli Town, Ledong County. Students are all from rural areas, and their foundation and study habits are relatively poor. Students are not adapted to the new classroom teaching methods; However, under the guidance of the new teaching concept, the old teaching methods and learning methods gradually fade away, but cultivate students' ability of observation, comparison, induction, independent exploration and cooperation and communication. Now, the class has initially formed a good study style of cooperative inquiry, and the classroom atmosphere of mutual evaluation between students and interaction between teachers and students has gradually formed.
Four. teaching process
(a) issues and situations
We are familiar with the operation of positive numbers, but in practical problems, the number of additions may exceed the range of positive numbers. For example, in football round robin, the number of goals scored is usually positive and the number of goals conceded is negative. Their sum is called goal difference. In the preface, the red team scored 4 goals and lost 2 goals; The blue team scored 1 and lost 1. So the red team's goal difference is
4+(-2),
The goal difference of the yellow team is
1+(- 1)。
The addition of positive and negative numbers is used here.
(2) Teachers and students explore the law of addition of rational numbers.
Earlier, we learned some basic knowledge about rational numbers, and today we will learn the operation of rational numbers. In this lesson, we will learn the addition of two rational numbers.
How many different situations are there when two rational numbers are added together?
To this end, let's look at a familiar practical problem:
In a football match, the number of wins is opposite to the number of losses. If we stipulate that winning is. Positive? What is the loss? Negative? , tied? 0? For example, winning 3 balls is +3, losing 1 ball is-1. The school football team may win or lose the game in the following different situations:
(1) won 3 goals in the first half and 1 goal in the second half, so the whole game won 4 goals. namely
(+3)+(+ 1)=+4.
(2) conceded 2 goals in the first half, 1 goal in the second half and 3 goals in the whole game. namely
(-2)+(- 1)=-3.
Now, please tell me other possible situations.
A: I won three goals in the first half, lost two goals in the second half, and won 1 goal. That's it.
(+3)+(-2)=+ 1;
Lost 3 goals in the first half, won 2 goals in the second half, lost 1 ball, that is to say,
(-3)+(+2)=- 1;
I won three goals in the first half and three goals in the second half, that is to say,
(+3)+0=+3;
Two goals were conceded in the first half, and neither team scored in the second half. In other words, two goals were conceded in the whole game.
(-2)+0=-2;
The first half was tied, the second half was tied, and the whole game was tied, that is to say,
0+0=0.
Above, we listed seven different situations of adding two rational numbers, and according to their specific meanings, we got the sum of their addition. However, to calculate the sum of two rational numbers, this method cannot always be used. Now, please observe and compare these seven formulas carefully. Can you find the algorithm of rational number addition from them? That is, how to determine the sign of the result? How to calculate the absolute value?
Here, let the students think first, communicate with teachers and students, and then summarize the rational number addition rule by themselves:
1. Add two numbers with the same symbol, take the same symbol, and add the absolute values;
2. Add two numbers with different absolute values, take the addend symbol with larger absolute value, subtract the smaller absolute value from the larger absolute value, and add two numbers with opposite numbers to get 0;
When a number is added to 0, it still gets this number.
(C), the application of example variant exercises
Example 1 Answer the result of the following formula
( 1)(+4)+(+3); (2)(-4)+(-3); (3)(+4)+(-3); (4)(+3)+(-4);
(5)(+4)+(-4); (6)(-3)+0; (7)0+(+2); (8)0+0.
After the students answered the questions one by one, the teacher and the students came to the same conclusion.
To add rational numbers, we must first judge whether two addends are the same sign or different sign, and whether one addend is zero; Then, according to the specific conditions of the two addend symbols, certain addition rules are selected. When calculating, it is generally necessary to determine first. And then what? Symbol, and then calculate? And then what? Absolute value of.
Example 2 (textbook example 1)
Solution: (1)(-3)+(-9) (two addends have the same sign, and are calculated according to the second law of addition).
=-(3+9) (minus sign, plus absolute value)
=- 12.
(2)(-4.7)+3.9 (addends with different symbols are calculated according to the second law of addition)
=-(4.7-3.9) (and take the negative sign to subtract the small absolute value from the large absolute value)
=-0.8
Example 3 (textbook example 2) After the teacher worked out the goal difference of the red team, the students worked out the goal difference of the yellow team and the blue team themselves.
Now, please calculate the following questions and exercises on page 23 of the textbook 1 and 2.
( 1)(-0.9)+(+ 1.5); (2)(+2.7)+(-3); (3)(- 1. 1)+(-2.9);
Students' written exercises, four students' performances, teachers' patrol guidance, students' exchanges, and teachers' and students' evaluations.
(iv) Summary
1. What did you learn in this class?
2. What do you think of this course? (Students summarize themselves)
(5) Practical design
1. Calculation:
( 1)(- 10)+(+6); (2)(+ 12)+(-4); (3)(-5)+(-7); (4)(+6)+(+9);
(5)67+(-73); (6)(-84)+(-59); (7)33+48; (8)(-56)+37.
2. Calculation:
( 1)(-0.9)+(-2.7); (2)3.8+(-8.4); (3)(-0.5)+3;
(4)3.29+ 1.78; (5)7+(-3.04); (6)(-2.9)+(-0.3 1);
(7)(-9. 18)+6. 18; (8)4.23+(-6.77); (9)(-0.78)+0.
4. use? & gt？ Or? & lt？ Fill in the blanks:
(1) If A >；; 0, b>0, then a+b _ _ _ _ 0;
(2) If
(3) If a>0, b<0, | a | & gt|b|, then A+B _ _ _ _ 0;
(4) If
Reflections on the addition teaching of rational numbers in seventh grade mathematics 1. Introduction of problems: Talking about the introduction of problems. The new curriculum standard should proceed from reality and make students have a strong thirst for knowledge. I adopted the question of small-scale military reconnaissance of our army by the enemy, and put the students in the role of commander. Put forward methods to solve problems, and do practical operations in various situations put forward by students, so that students can understand the application of mathematics in solving practical problems. The introduction of sensory problems is too simple and the scope of students' thinking is too limited. There is no warm learning atmosphere. Therefore, the introduction of questions should be deep and challenging.
Second, the inquiry of the problem: In the inquiry of the problem, I used a villain to walk back and forth on the coordinate axis, which produced a dynamic effect, allowing students to have more time and space under the situation provided by the teacher, and to participate in the inquiry and discovery in person and take the initiative to acquire knowledge and skills in the state of curiosity. However, there are also some problems in the whole implementation process. For example, there are some problems in students' summary of the law. When I dealt with it again, I answered the students' questions because I was afraid of not having enough time. In fact, it should be solved by students themselves, which is very helpful to improve students' ability.