1. Students begin to operate. By measuring, cutting, spelling and folding, they explored and found the rule that the sum of the internal angles of a triangle is equal to 180 degrees.
2. In the process of inquiry, experience the process of knowledge generation, development and change, and cultivate strategic awareness and preliminary spatial thinking ability through communication and comparison.
3. Experience the process and method of inquiry, feel the process of improving thinking, and stimulate curiosity and interest in exploration.
Teaching focuses on the process of discovering and verifying the law of "triangle internal angle and 180 degrees" and summarizing the law.
Teaching difficulties lead to different inquiry methods and students' flexible application rules.
Prepare teaching AIDS, courseware and tables. Students prepare different types of triangles and protractors.
teaching process
First, stimulate the introduction of interest.
1, riddle
Teacher: Do students like guessing riddles?
Health: Yes.
Teacher: Then, the teacher gives you a riddle. Please listen to this riddle:
Shaped like a mountain, steady and solid, the three poles are connected end to end, and learning is not simple. (Rushing at a number) What did you say together?
Health: triangle
2. Introduce the classification of triangles by angle.
Teacher: How clever! ! The blackboard "triangle"! Then, triangles can be divided into obtuse triangles, right triangles and acute triangles according to their angles.
Show the cards and stick them on the blackboard.
3. Stimulate students to explore their own hearts.
Teacher: Can you draw a triangle?
Health: Yes.
Teacher: Please take out your pen and draw a triangle on your notebook, but I have one request: draw a triangle with two right angles. Give it a try!
Student: Try to draw.
Teacher: Did you draw it?
Health: No.
Teacher: You can't draw, can you?
Health: Yes.
Teacher: Why can't you draw a triangle with two right angles? This is the mystery of the middle corner of the triangle! In this lesson, we will learn the knowledge of triangle interior angles, "the sum of triangle interior angles" (blackboard writing topic)
Second, explore new knowledge.
1, know the inner angle of the triangle.
Look at these three words. What is the inner angle of a triangle?
Health: It's the angle inside the triangle.
Teacher: How many internal angles does a triangle have?
Health: three.
Teacher: Then, for the convenience of research, we use angle 1 angle 2 and angle 3 to mark these three internal angles, and ask the students to take out the triangle on the table (marked by the teacher).
Teacher: Do you know what the "sum of interior angles" of a triangle is?
Health: the degree of addition of the inner angles of a triangle.
2. Study the sum of internal angles of special triangles.
Teacher: Take out a right triangle respectively. Please look at what triangle this belongs to and say the degree of each angle. What is the sum of the internal angles of this triangle?
Student: Let's calculate: 90+60+30 =180 90+45+45 =180.
Teacher: 180 is also what angle we have learned?
Student: Boxer
Teacher: What did you find from the calculation of the sum of the internal angles of the two triangles just now?
3. Study the sum of internal angles of general triangles.
Teacher: Guess, what is the sum of the internal angles of other triangles?
Health:
4. Operation and verification
Teacher: Students' guesses are different. What shall we do? Can you find a way to verify it?
Requirements:
(1) Every 4 people are a group.
(2) Each team has different types of triangles, and each type needs to be verified. Let's discuss how to finish the task quickly.
(3) There is more than one way to verify, so students should think more.
Teacher: OK, let's start our activities!
Teacher: patrol guide
Teacher: OK! Ask a group of people to report the measurement results.
Health: Through measurement, we found that the sum of the three internal angles of each triangle is about 180 degrees.
Teacher: Actually, the sum of the interior angles of a triangle is 180 degrees. It is only because there are some errors in our measurement that the measurement results are inaccurate.
Health: I tear off the three inner angles of a right triangle by tearing, and put them together to make a right angle, which is 180 degrees.
Teacher: OK! Very good!
Teacher: Are there any other students who operate acute triangles and obtuse triangles? Who wants to show it in front? Health: acute triangle (tearing)
Student: Tell me how to fold it. I fold the three angles of an acute triangle together to form a right angle, which is 180.
Teacher: The teacher also did an experiment to see if it was the same as everyone's result. (Multimedia presentation)
Now the teacher asks the students, what is the sum of the inner angles of the triangle?
Health: 180 degrees.
Teacher: Through verification, we know that the sum of internal angles of acute triangle, right triangle or obtuse triangle is 180. Blackboard: The sum of the internal angles of the triangle is equal to 180 degrees. Now let's read our discovery with pride and affirmation: "The sum of the inner angles of the triangle is 180".
Third, solve the problem.
Teacher: OK! Please recall, did the teacher ask the students to draw a triangle with two right angles just before class?
Health: No.
Teacher: Then can you explain why you can't draw it with the knowledge of this lesson?
Health: Two right angles are 180 degrees. There is no third angle.
Teacher: I want to draw two obtuse triangles. Can you draw them?
Health: If it is greater than 180 degrees, the third angle will not be drawn. Teacher: So, there is no such triangle in life.
Teacher: Once we have learned knowledge, we must know how to use it.
Fourth, consolidate and improve.
1, fill in the blanks.
The sum of the internal angles of a (1) triangle is () degrees.
(2) The two internal angles of the triangle are 80 and 75 respectively, and the other angle is ().
2. Find the degrees of the following angles.
(1)≈ 1 = 27∠2 = 53∠3 = () This is a triangle ().
(2) ∠ 1 = 70 ∠ 2 = 50 ∠ 3 = () This is a triangle.
3. Judge whether the three angles in each group are three internal angles in the same triangle.
( 1)80 95 5 ( )
(2)60 70 90 ( )
(3)30 40 50 ( )
4. The red scarf is an isosceles triangle. Find the degree of the base angle. (Multimedia presentation)
Educate students to think about quality.
5, thinking extension.
According to the sum of the internal angles of a triangle is 180 degrees, what is the sum of the internal angles of a quadrilateral and an octagon?
6. Game: Help the corner find friends. Which three corners in each deck can form a triangle? ) Which three corners in each deck can form a triangle? )60 90 45 30 ⑴60 、90 、45 、30 54 46 52
Verb (abbreviation of verb) summary.