1, the quotient of the circumference and diameter of a circle is called (), which is represented by the letter ().

2. In an equal circle, all diameters are (), all radii are (), and diameters are radii ().

3. When the diameter of a circle is tripled, its circumference is multiplied by () times and its area is multiplied by () times.

4. The rectangle has a () axis of symmetry. A square has () axis of symmetry, an isosceles triangle has () axis of symmetry, and a circle has () axis of symmetry.

5. Draw the largest circle in a square with a side length of 4 decimeters. This circle has a diameter of () decimeter, a radius of () decimeter, a circumference of () decimeter and an area of () square decimeter.

6. Divide a circular piece of paper with a diameter of one centimeter into several equal parts and cut it into an approximate rectangle along the radius. The circumference of a rectangle is () cm, the radius of a circle is () cm, and the area is () cm2.

7. The radius of a big circle is six times that of a small circle, the circumference of a small circle is () of a big circle, and the area of a big circle is () of a small circle.

8. The circumference of a semicircular flower bed is 30.84 meters, and the area of this semicircular flower bed is ().

Second, judge.

1, the circumference of a circle is twice its radius. ( )

2. The diameter of a circle is the symmetry axis of this circle. ( )

3. The circumference of a semicircle is half that of a circle with the same radius. ( )

4. The line segment passing through the center of the circle is called the diameter. ( )

A circle with a radius of 2 cm has the same circumference and area. ( )

6. If the diameter of a circle is equal to the side length of a square, then the area of the square is smaller than the area of the circle. ( )

Third, choose.

1. Draw the largest circle in a rectangle with a length of 6 cm and a width of 4 cm. The area of this circle is () square centimeters.

( 1)28.26

(2) 19.625

(3) 12.56

2. The radius of a circle is 1 decimeter, and its semicircle circumference is () cm.

( 1)3. 14

(2)4. 14

(3)5. 14

3. If the diameter of a circle is enlarged by 6 times, its area will be ().

(1) 6 times larger

② 36 times larger.

(3) The magnification is 12 times.

Fourth, answer the following questions.

1. Through a bridge, a wheel with a diameter of 1.2m needs to turn 500 times. How long is this bridge?

2. There are two circles, a big circle and a small circle. The circumference of the small circle is 37.68 meters, and the diameter of the big circle is twice that of the small circle. What is the area of the great circle?

The circumference of a square is equal to the circumference of a circle. The side length of a square is 12.56 meters. What is the area of a circle?