1. Status and function: The main content of this lesson is the concept of score, and the conditions for mastering the meaning of score and the value of score is 0. On the basis of students' mastery of four algebraic operations and polynomial factorization, and on the basis of fractional knowledge learned in primary schools, it introduces the concept of fraction by comparison, and expands students' understanding of "formula" from algebraic to rational. Learning the knowledge of this lesson well is a step forward.

2. Analysis of learning situation: Students may use the thinking formula of learning score to know and understand the score, but in the score, its denominator is no longer a specific number, but an abstract algebraic expression with letters, which will change with the change of letter value.

3. Teaching objectives: According to the actual situation of students in our school, I have determined the teaching objectives of this class as follows:

(1) Knowledge and skill objectives: ① Understand the concept of mastering scores; ② We can find the condition that the score is meaningful and the value of the score is 0.

(2) Process and Method Objectives: ① Through the analogy between fractions, students can experience the process of expanding from algebra to fractions, and initially learn to study mathematical problems by analogy; ② Students have improved their understanding of the dialectical view that things are universal connections, changes and developments through analogy.

(3) Emotion, attitude and values: ① Combining with practice, exploring the concept of score, and realizing the application value of mathematics; In the process of cooperative learning, enhance the sense of cooperation with others.

4. Teaching emphases and difficulties:

Key point: the concept of score.

Difficulties: Understand and master the conditions that the score is meaningful, meaningless and the value of the score is 0.

The key to highlight the key points and break through the difficulties: some students tend to ignore the condition that the denominator of the score cannot be 0, so we should adopt the meaning of analogy score in teaching and strengthen the teaching that the denominator of the score cannot be 0.

Second, teaching methods and teaching materials processing

1. Teaching methods

Through the familiar real life scenes, students find that some quantitative relations can not be expressed by algebraic expressions only, which leads to cognitive conflicts and puts forward a strong desire to learn new knowledge. Guide students to explore the concept of fractions by analogy and form interaction between teachers and students, which shows that mathematics teaching activities must be based on students' cognitive development level and existing knowledge and experience.

2. Guidance of learning methods In the guidance of learning methods in this class, I will adopt the learning methods of group cooperation, discussion and exchange, observation and discovery, and teacher-student interaction. Through group cooperation, students can learn to actively explore, summarize and improve, highlighting that students are the main body of learning.

Third, the teaching process design

1. Create a situation

Because mathematics comes from life and serves life, I introduced three life examples, in which the answer to the first question is algebraic, while the answers to the second and third questions can no longer be expressed in algebraic terms, and letters appear in the denominator, which is different from the algebraic expressions learned in the past. So I asked: What are the similarities and differences between the answers to these two questions and the scores in our primary school? This aroused students' interest, stimulated students' interest in exploration, and then led to the topic of this lesson-the concept of score.

Form a concept

17. 1. 1 The concept of fraction is presented under the guidance of my question, so that students can carefully observe the expression forms of the answers to the second and third mini-questions, which are very similar to the expression forms of fractions learned in primary schools, but they are different. Let students observe the differences, organize students to discuss, cooperate and communicate, and let students show their findings in groups in front of their classmates. Denominators all contain letters; As long as the two formulas are divided, it is a fraction and so on. According to the results of students' inquiries, I summarized them, and then got the concept of score. That is, a formula in the form of (A and B are algebraic expressions, B contains letters, and B≠0) is called a fraction, where A is called the numerator of the fraction and B is called the denominator of the fraction. In order to deepen students' personal understanding of the concept, I will explain the concept of score as follows: 1 Fractions can be understood as division symbols, including the role of parentheses. However, the denominator of a fraction must contain letters. 3. The denominator of the score must be non-zero, otherwise it is meaningless. At the same time, correct the wrong idea that the score is the score as long as the two formulas are divided. In order to show students' autonomy and stimulate their interest in learning, let students give some examples of scores.

3. Consolidate training

According to the learning needs of different students and the teaching principle of gradual progress, I first arranged a concept training example 1, which aims to let students understand the concept, consolidate the concept and highlight the key points of this lesson. Because algebra and fraction appeared in the training, I gave the concept of rational expression in this link, that is, algebra and fraction are collectively called rational expression. In order to deepen the understanding of the concept of fraction again, I gave example 2. However, the title is changed to "Conditions for Finding Meaningful Scores", and its purpose is still to let students understand the concept of scores. In order to expand students' thinking ability and lead to the difficulties in this lesson, I give two thinking questions: thinking questions 1 is to make students think about under what circumstances scores are meaningless, which reflects the ability of reverse thinking in mathematics. Thinking question 2 is to let students think about how to make the score value 0 first. Because students are unfamiliar with new knowledge, they can answer as long as the numerator is 0 under the fixed thinking. At this time, I will guide students to re-understand the concept of score. If the denominator is not 0, it is meaningful to require the numerator to be 0 first, otherwise it is meaningless. This leads to example 3, which emphasizes that the numerator is 0 again, that is, the denominator is not 0 and the numerator is 0, while ensuring the significance of the score. In this way, the difficulty of this course has been broken. In order to better understand and master the difficulties of this lesson, there are two consolidation exercises at different levels from low to high, hoping that students can turn knowledge into skills. Consolidation training is the comprehensive application of meaningless score and zero score, and it is the training to improve students' comprehensive ability. Second, consolidation training is thinking expansion, which can expand students' divergent thinking. According to the condition that the fractional value of this lesson is 0, most students can think that as long as the denominator is not 0 and the numerator is 0, that is, (x-2)(2x+5)≠0 and x-2=0, it can be concluded that the fractional value cannot be 0. However, some students may ask the following questions: because the denominator of the molecule contains factors, in the result of simplification, the molecule gets 1, so the fractional value must not be 0. I fully affirm the students' ideas and explain them. Because (x-2)(2x+5)≠0 is meaningful and (x-2) must not be 0, the numerator and denominator can be omitted at the same time.

Step 4 summarize your homework

Students summarize, summarize and reflect, deepen their understanding of knowledge and skillfully use what they have learned to solve problems.

In the teaching practice of this class, many conclusions try to guide students to explore, highlight the main position of students' activities and reflect students' main position in teaching. At the same time, I hope that students can master the hierarchical and progressive learning method and use this method in future study.

The knowledge structure I adopted in this class is: first, create problem situations, introduce examples, ask questions, form concepts by analogy, strengthen feedback training and consolidate, and finally summarize. The whole process conforms to the cognitive law of junior high school students.

Fourthly, some thoughts on the teaching process.

1. Reflections on teaching design: create a good learning atmosphere and stimulate students' curiosity through students' familiar life situations.

2. Thinking about the formation of concept: analogize the definition of score, get the concept of score, and highlight the key points.

3. Formation of thinking skills: Through different levels of training, students can have a clearer understanding of scores, expand their thinking and achieve the established teaching objectives.

4. Thinking about induction and summary: Through students' induction, summary and reflection, students' generalization and expression ability can be improved.