Teaching objectives:
1. In the activities of hands-on, measurement and discussion, I experienced the process of exploring the trilateral relationship of the triangle.
2. Further understand the triangle, understand the relationship between the three sides of the triangle, and know that the sum of any two sides of the triangle is greater than the third side.
3. Actively participate in exploration activities and experience the challenges of mathematics and the certainty of mathematical results.
Teaching preparation:
Teacher: A triangle, a proofreading board marked with length.
Student:
1.4 sheets of paper, with lengths of 4cm, 5cm, 8cm and10cm respectively.
2. study papers.
Teaching process:
First, the problem situation
1, review the characteristics of triangles.
Teacher: Students, we already know the triangle. What do you know about triangles?
Health 1: A triangle has three angles, three sides and three vertices.
Health 2: There are right triangles, obtuse triangles and acute triangles.
Health 3: There are equilateral triangles and isosceles triangles. (Comment: This question is to understand students' understanding of the cause. )
2. Further understand the triangle.
Teacher: Students know the characteristics of so many triangles, so who can tell what the triangle is like in one sentence?
A figure with three sides, three angles and three vertices is a triangle.
Teacher: The students just talked about the characteristics of triangles. Then let's think about it. What are the three sides of a triangle?
Health: Three lines.
Teacher: Yes! Therefore, we can say that the figure surrounded by three line segments is called a triangle. (Written on the blackboard) Who will say something? Let's read together. (Comment: This process is based on the students' language development level, and under the guidance of teachers, the definition of triangle is abstracted, which conforms to the law of cultivating students' cognitive development. )
Teacher: What does "encirclement" mean here?
Health 1: connection.
Health 2: Together.
Health 3: Get together.
Teacher: Look, can such a figure be called a circle? The teacher drew a figure with a gap.
Health 1: No, because there is still an opening on it.
Health 2: We can't get along.
Teacher: I see, it must be connected to form a circle, so the figure surrounded by three lines is called a triangle. (Comment: The word "surround" is difficult for students to understand. Teachers should help students. Teacher Zhang did a good job, but it should be emphasized that it would be better if the three lines were connected end to end. )
Second, hands-on operation
Teacher: We know that a triangle is surrounded by three lines. Can any three lines form a triangle?
Health 1: Yes!
Health 2: No, two of them must be longer than the third.
Teacher: Some students think "yes", while others think "no". If we want to know the result, we must try again. Before class, the teacher prepared four sticks, the lengths of which were 4cm, 5cm, 8cm and10cm. Please choose three sticks to make a triangle at a time and see if you can make it every time.