The teacher cuts the prepared radish with a knife, guides the students to observe, and lets the students fully imagine and answer what kind of cross section it is; Using multimedia demonstration, let students observe the shape characteristics of the obtained section. Let all students understand the meaning of section (section).

The meaning of section: cut one by one, and the cut place is called section.

Activity 2 Activity 2: Explore and learn new knowledge.

(1) Active operation 1: Cut the cube with a plane.

Ask a question: what shape cross section can be obtained by cutting a cube with a plane?

Guide students to make bold guesses and let them imagine the possible shape of the cross section. Let the students discuss in groups and cooperate with each other. Encourage students to speak actively and answer questions.

Teachers guide students to practice, cut carrots in groups, and encourage students to test their guesses from the cutting activities.

Teachers patrol students in student operation activities, participate in students' discussion and exchange, and encourage students to express their opinions boldly in group activities.

At the end of the class's physical cutting activity, the teacher encouraged each group in the cutting activity to invite representatives to speak, actively encouraged them to tell how many different parts they could cut, and selected some groups for them to demonstrate. And positively affirm their practices.

Teachers actively encourage each group to invite representatives to speak, tell them the process of producing and changing various shapes of cross-sections observed by using experimental operation courseware, and explain why different cross-sections are produced in their own language. Positive affirmation of students' correct reasoning.

Summarize the students' speeches. Affirm the students' correct statements

Guide students to discuss:

Cut a cube with a plane:

1. Is it possible that the cross-sectional shape is triangular? Could it be a triangle with three equal sides?

2. Is it possible for the cross-sectional shape to be quadrilateral? Could it be an isosceles trapezoid?

3. Is the cross-sectional shape possibly pentagonal? Is it possible that the cross-sectional shape is hexagonal?

4. Is it possible that the cross-sectional shape is a heptagon?

When a plane cuts a cube, the cross section obtained is the result of the intersection of this plane and several planes of the cube. If an edge intersects with three faces, the section is _ _ _ _ _; If it intersects with four faces, the section is _ _ _ _ _; If it intersects with five faces, the section is _ _ _ _ _; If it intersects with six faces, the section is _ _ _ _.

Teachers actively encourage each group to invite representatives to speak, tell them the process of producing and changing various shapes of cross-sections observed by using experimental operation courseware, and explain why different cross-sections are produced in their own language. Positive affirmation of students' correct reasoning.

Summarize the students' speeches. Affirm the students' correct statements

(2) Activity operation 2: Cutting cylinder or cone with plane.

Thinking: what shape will the cross section be when cutting a cylinder or cone with a plane?

(3) Application of knowledge:

1, let the students finish the textbook page 13, think about it and say what the cross section is.

The section of figure (1) is: the section of figure (2) is:

The cross section of Figure (3) is: The cross section of Figure (4) is.

The teacher suggested that cutting a geometry knowledge plays a great role in real life.

2. Let the students read the textbook 15: Do you know CT? Let students experience the application of mathematics knowledge in real life.

[Teacher's Activity]: Ask the students and talk about reading: Do you know CT? After the experience, talk about the connection between mathematics knowledge and real life, let students speak freely and stimulate their enthusiasm for learning mathematics.

Knowledge expansion:

Cut geometry with a plane. If the cross section is circular, can you imagine what the initial geometry is?

(a: spherical cylindrical truncated cone)

Activity 3 Exercise 3. class exercise

Complete the exercises on page 14 of the textbook.

Complete the knowledge and skills on page 0/5 of the textbook/kloc-.

Activity 4 Activity 4, Class Summary

Question: What did you learn from this course? What are your experiences?

The cross section of a cube can be triangular, quadrilateral, pentagonal or hexagonal. To cut out several polygons, you only need to make the tangent plane intersect with several faces. To cut out a special polygon, you only need to adjust the direction of the incision.

The cross section of geometry consists of the intersection line between plane and geometric surface.

Activity 5, homework 5. homework

1. According to the chart, tell the shape of the section.

2. Answer questions:

(1) is a cuboid as shown in the figure. What geometry can be cut from it?

(2) Cut a geometric figure with a plane. If the cross section is triangular, can you imagine what the initial geometry is?

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Activity 6 After-class Test

After-school test:

1, true or false

1). Cut the cube with a plane, and the section must be square or rectangular. ()

2). Cut the cylinder with a plane, and the section must be round. ()

3). Cut the cone with a plane, and the section must be triangular. ()

4). Cut the ball with a plane. No matter how you cut it, the section is round. ()

2. Choose and fill in the blanks:

1), as shown in the figure, cut a cube with a plane, and the cross-sectional shape obtained should be ().

2), in the following geometry, the profile can't be a circle ()

A. cylinder B. cone C. sphere D. cube

3), as shown in the figure, cut the cone with a planer, and the cross-sectional shape obtained is ().

4) Cut a cube with a plane. If the obtained section is a triangle, the larger geometry on the left must have a ().

A.7 face B. 15 edge C.7 vertex D. 10 vertex

5), as shown in the figure, use a plane to cut the cylinder, and the cross-sectional shape is ().

6), with a plane cutting cylinder, its cross section shape can't be ().

A. circle B. cube C. cuboid D. trapezoid

7), cut a cube with a plane, the cross section shape may be _ _ _ _. (Write all possible shapes)

3. Answer questions:

1) If a cone is cut by a plane, can the cross section be triangular? Could it be a right triangle? When the cross section is circular, is it possible that the cross section area is exactly equal to half of the bottom area?

2) Try it: Can you get an equilateral triangle by cutting a cube with a plane? Can you cut a right triangle or an obtuse triangle section?

3) Cut off a part of the quadrangular prism with a plane. Please draw a picture to show that the remaining part may still be a quadrangular prism.

4) A cuboid container contains a certain volume of water with a layer of yellow oil floating on it. If you tilt the container in different directions, you can observe an image similar to a slice. Just try it. What kind of part do you see?

5) If a cylinder is cut by a plane, can the cross section obtained by (1) be triangular? (2) If a square section can be obtained, what is the relationship between the radius of the bottom surface of the cylinder and the height?

6) Cut a geometric figure with a plane. If the cross section is square, can you imagine the original shape of this geometry?