Radius r of a circle

Diameter d of a circle

Circumference c of a circle

Area s of a circle

2 cm

2 cm

18.84 cm

8 cm

Second, think about it and fill it out.

1. When the distance between two feet of the compass is 4 cm, the circumference of the circle drawn is () cm.

2. Draw the largest circle on a rectangular paper with a length of 8 cm and a width of 12 cm. The diameter of this circle is (), the area is () and the circumference is ().

3. The diameter of a wheel is 55 cm, and the wheel rotates once, about () meters forward.

4. The diameter of the outer circle of a ring is 10cm, the diameter of the inner circle is 8cm, and the area is () cm2.

5. The radius, perimeter and area of the circle are enlarged by 2 times, () times and () times respectively.

Third, please be a small referee.

1, the center of the circle determines the position of the circle, and the radius determines the size of the circle. ( )

2. When the radius of a circle is equal to 2 decimeters, the circumference and area of the circle are equal. () 3. The area of a circle is equal to the area of a square, and their perimeters must be equal. () 4. The diameter of the same circle must be twice the radius. () 5. The line segment with two ends on the circle has the largest diameter. () 6. The circumference of a semicircle is half that of a circle. ( )

Fourth, choose one. (Choose the serial number of the correct answer and fill in the brackets)

1，pi () 3. 14。 A, greater than B, equals C, less than.

2, in the following figure, the symmetry axis is the most ().

A, isosceles triangle b, square c, circle

3. The circumference of a circle is 3 1.4 decimeter, and the area of this circle is () decimeter 2.

a、3 14 B、78.5 C、 15.7

4. A semicircle with a radius of r and a circumference of ().

a、πr + 2r B、πr C、π/4

5, square, rectangle and circle with equal perimeter, () has the largest area.

A, square b, rectangle c, circle

Fifth, do as required.

1. Please draw a circle with a compass with a diameter of 3 cm.

Please draw the symmetry axis of the picture below.

6. Calculate the area below.

Seven, solve the problem.

1. The minute hand of the watch is 5 cm long. What is the distance traveled by the minute hand tip in 2 hours?

2. The bowling radius is about 1dm, and the fairway length is about 18m. How many times should bowling be rolled from one end to the other?

3. A flower bed with a diameter of 5 meters is surrounded by a circular path with a width of 1 meter. What is the area of this path?

4. There is a circular lawn with a circumference of 62.8 meters, and it is ready to install an automatic rotary sprinkler irrigation device for sprinkler irrigation. There are three types of devices with a range of 20m,15m and10m. Which do you think is more suitable? Where is it installed?

Just try it. ※.

There is a plum flower bed in the center of the square, and the outer circle is five semicircles, each with a radius of 2 meters. What is the circumference of this flower bed?