Teacher: In the triangle family, the three brothers have always been United and friendly, but today they quarreled over some trivial matters. Let's go and see what happened.

Teacher: Children, do you know what they are fighting for from their conversation?

Health: the sum of the angles in a triangle.

Teacher: You listened carefully! Everyone knows that a triangle has three angles, and these three angles are the inner angles of the triangle. If the degrees of the three angles of a triangle are combined, it is called the sum of the inner angles of the triangle. So who do you think has the biggest internal angle sum among the three brothers?

Health: ......

Teacher: Is that right? Today, in this lesson, we will explore the sum of the inner angles of the triangle (show the topic).

Teaching objectives:

1. Through reasoning, transformation and other activities, let students experience the process of discovering and proving that the sum of the internal angles of a triangle is equal to 180 degrees.

2. We will make some simple calculations and inferences by using the conclusion that the sum of the internal angles of the triangle is equal to 180 degrees.

3. Experience the joy of success in the process of hands-on experiment, exploration and discovery, thinking and reasoning, and then cultivate students' exploration spirit and practical ability.

Teaching process of triangle interior angle sum;

Hierarchical practice design can train students' thinking flexibility, give them an opportunity to show themselves and make their personalities known, make them master new knowledge skillfully, have the opportunity to experience the joy of success and understand that there is mathematics everywhere in life.

1, measure a quantity: each student adds up the degrees of the sum of the internal angles of the triangle that he has just measured, and initially draws the conclusion that the sum of the internal angles of the triangle is 180.

2. Folding: Fold the square paper diagonally to make it into two completely coincident triangles. It is found that the sum of the internal angles of the triangle is half of the sum of the internal angles of the four corners of the square, that is, half of 360, that is, 180 degrees, which preliminarily verifies the conclusion that the sum of the internal angles of the triangle is 180.

3. Spelling: Students will first spell the prepared triangle, and further verify the conclusion that the sum of the internal angles of the triangle is 180.

4. The teacher used courseware to demonstrate the process of turning three corners of a triangle into a right angle.

5. Verification: FLASH demonstrates the process of cutting and repairing three triangles.