(1) The teacher connects point A and center O, point B and center O with crayons ... and connects arc AB with crayons, and then draws the fan with crayons.

Ask questions:

(1) Painted with colored graphics is a bit like something in our daily necessities? (Fan)

(2) It is a part of a circle. What is the figure surrounded by?

(3) According to the students' answers, it is concluded and revealed that the sector is surrounded by two radii on a circle and a curve (arc).

Instruct students to practice. Draw a fan in the circle you just met.

Show the exercise 1 by projection, and ask the students to explain the reasons when they answer.

Continue to understand the relationship between sector and triangle. Question: Think about it. What's the difference between a sector and a triangle?