Subject: Axisymmetric Graphics
What I'm talking about today is axisymmetric graphics. This lecture is divided into five parts. Let me talk about the first part.
I. Presentation materials
1, teaching material analysis: "Axisymmetric graphics" is the teaching content of Unit 5 of the first volume of the second grade of the nine-year compulsory education People's Education Edition. Symmetry is one of the structural patterns of nature, which exists widely in our daily life and has many forms of transformation. Understanding axisymmetric graphics plays an important role in cultivating students' observation and aesthetic ability. Based on the above understanding, I set the following teaching objectives:
Knowledge goal: Students can observe, operate and understand axisymmetric figures, cut out simple axisymmetric figures with scissors, understand and draw the symmetry axis.
Ability goal: cultivate students' observation ability and operation ability, and learn to appreciate the beauty of mathematics by watching and folding.
Emotional goal: in the process of understanding, making and appreciating symmetrical figures, feel the symmetrical beauty of objects and figures, and stimulate students' enthusiasm for learning mathematics.
3. The focus of teaching is to understand the characteristics of axisymmetric graphics, and the difficulty is to draw the symmetry axis of symmetric graphics.
4, teaching aid preparation: pictures, paper, scissors.
5. Prepare school tools: rectangular paper and scissors.
Second, oral teaching methods
According to the new curriculum concept, students' existing knowledge and life experience, combined with the characteristics of teaching materials, I adopted the following teaching methods.
1. Situational teaching method: At the beginning of the new class, students can initially perceive the beauty of symmetry, which can stimulate their interest in learning, and then design a scene to cut symmetrical graphics, which can arouse their enthusiasm for exploring symmetrical graphics.
2. Demonstration method: With the full help of the visual demonstration of pictures, students' perceptual knowledge can be effectively enhanced and the essence of axisymmetric graphics can be better grasped.
Third, theoretical study.
Hands-on practice, independent exploration and cooperative communication are important ways for students to learn mathematics. Practical operation, independent inquiry and observation are also the main methods for middle school students to learn new knowledge in this course.
Fourth, the teaching process
Reasonable arrangement of teaching process is one of the keys to successful teaching. I will arrange the following five steps for the second-year students to complete the teaching under the guidance of the new curriculum standard and by means of cooperative inquiry and hands-on operation.
(1) Create situations and introduce new lessons. When introducing the new class, I will show two images. The first image is asymmetrical and the second image is symmetrical. Ask the students to compare by observation. Which image looks good and why? Students will definitely say that the second image looks good, because the left and right sides of the face in the second image are exactly the same. At this time, I skillfully set up a suspense-like the second image, starting from the middle, what is the name of the exactly the same figure on the left and right sides in teaching? Through the study of this book, students will certainly understand. In this section, I will let the students have a look and compare. Feel the beauty of symmetry initially, let the students talk about it, and arouse their enthusiasm for learning.
(2) Take a look, fold and explore symmetry.
First of all, I show a group of symmetrical objects (dragonflies, leaves, butterflies, masks) that are common in daily life, so that students can observe with questions: What are the characteristics of these figures? Then guide the students to observe carefully. On the basis of students' careful observation, teachers and students concluded that these figures all started from the middle, and the left and right sides were exactly the same. This phenomenon is called symmetry in mathematics, and it is also the theme of blackboard writing-axisymmetric graphics.
It is a perceptual knowledge for students to observe the objects on the blackboard. In order to transform students' perceptual knowledge into knowledge in their minds, I designed such a link: give each study group two symmetrical figures (rectangles and squares), guide the students to fold the two figures in half, and then tell everyone what they found. Fold in half, and students will find that the two figures are completely overlapping left and right or up and down after folding in half. At this time, I am writing on the blackboard (after being folded in half-the left and right sides are completely reunited).
(3) cut it, draw a picture and feel the symmetry axis.
The development of children's thinking is the transition from concrete thinking in images to abstract thinking. Children learn knowledge and develop their abilities through various activities. Therefore, after students have a preliminary understanding of the characteristics of axisymmetric graphics, I arranged for students to cut a paper-cutting activity. In this session, I first ask: Students, through your understanding of axisymmetric graphics, can you cut out an axisymmetric graphic?
Then guide the students to see how to do it in the textbook. Then, I take the example of cutting clothes on page 68 of the textbook as an example to demonstrate and guide. During the demonstration, I told the students that cutting symmetrical figures is divided into three steps. The first step is to fold a rectangular piece of paper in half, and the second step is to cut it according to the dotted line. The third step is to unfold the folded paper into a symmetrical figure. Through the teacher's intuitive demonstration, let the students know the cutting method of symmetrical graphics and cut out their favorite symmetrical graphics. Students can cut out a symmetrical small tree, a symmetrical love and a symmetrical gourd. I show students' works, so that students can enjoy the fruits of their labor and experience the happiness of success. Through this kind of teaching, students can walk into practice with knowledge, apply knowledge in practice and develop their thinking.
After exhibiting the students' works, I asked the students to observe the exhibited works and ask questions. What are the similarities between these figures? Through observation, students will soon find that there is a crease in the middle of these figures, and the teacher leads the symmetry axis from the crease in the middle of the axisymmetric figure. (crease symmetry axis)
After students know the axis of symmetry, I will focus on guiding students to draw the axis of symmetry, which is the difficulty of this lesson. In order to break through the difficulties, I adopted an intuitive demonstration method, taking the small trees on display as an example. The teacher told the students while drawing the symmetry axis, emphasizing that the symmetry axis is represented by a dotted line, and guiding the students to draw the symmetry axis on their own works.
Mathematics comes from life and is also used in life. After students know symmetrical figures, let them find out which objects around them are symmetrical. Students may say that the blackboard desks in the classroom are symmetrical, the windows are symmetrical, and the teddy bears at home are symmetrical. Let students speak freely and experience the joy of learning.
(d) Consolidate the practical application of knowledge.