Teaching objectives:

1, through hands-on operation and observation, know the characteristics of the triangle and the meaning of the height and bottom of the triangle, and draw the height in the triangle.

2. Cultivate the ability of observation and operation and the ability of applying mathematical knowledge to solve practical problems.

3. Experience the connection between mathematics and life and cultivate students' interest in learning mathematics.

Teaching emphases and difficulties:

Know the triangle, know the characteristics of the triangle and the significance of the high and low of the triangle, and you will draw the height in the triangle.

Teaching preparation:

Teachers' preparation for the exam: thematic map related to teaching materials.

Student preparation: white paper, drawing tools.

Teaching process:

First, create scenarios and introduce new lessons.

1, showing the theme map on page 80 of the textbook.

2. What other objects have you found in your daily life?

Angular?

Since triangle is widely used in daily life, what are its characteristics and properties? This is what we will learn in this unit. Today, let's get to know the triangle first.

(1) Let the students draw a triangle.

(2) Students look at the triangles they draw. Who says a triangle has several sides, angles and vertices?

(3) Mark the edges, corners and vertices you refer to in the picture below.

(4) Mark the names of each part of the triangle according to the students' report on the blackboard.

(5) What are the characteristics of these triangles?

(6) What is the most obvious feature of a triangle?

(7) good. Now, can you summarize it in your own words? What kind of figure is a triangle?

(8) Students are noncommittal about various definitions. Let students see how the textbook defines triangles.

(9) Definition of blackboard writing triangle: a figure surrounded by three line segments (each phase

Endpoints of two adjacent lines are connected. ) is called a triangle.

Third, teach the height and bottom of a triangle.

1. Now, please take out the triangle you just drew and find a vertex perpendicular to the opposite side. (Teachers visit)

2. Demonstrate drawing a vertical line from the vertex of a triangle to its opposite side.

Let's give this vertical line a name. Blackboard writing: Draw a vertical line from the vertex of a triangle to its opposite side. The line segment between the vertex and the vertical line is called the height of the triangle, and the opposite side is called the bottom of the triangle.

Can you draw other heights and bottoms in the triangle just now?

Fourthly, teaching the representation of triangle.

1. If you need to draw a triangle, it will be very troublesome. Have you thought about it?

For the convenience of expression, we usually use letters A, B and C to represent the three vertices of a triangle (the teacher writes three letters on the triangle on the blackboard). This triangle can be represented as triangle ABC.

3. Point out: Of course, the three vertices of a triangle can also be represented by other letters.

Warm-up before class: Name the chart. Show pictures.

How high is the triangle?

Teaching reflection: this lesson is to let students further perceive the attributes of triangles in the operation of drawing triangles. The concept describes the definition of triangle in its own words, and the effect is good.