3. When the distance between the two feet of the compass is 4 cm, the circumference of the circle drawn is (25. 12) cm.
4. The radii of the two circles are 3cm and 5cm respectively, and their diameter ratio is 3:5, perimeter ratio is 3:5 and area ratio is 9:25.
5. The radius, perimeter and area of the circle are enlarged by 2 times, 2 times and 4 times respectively.
6. The diameter of the outer circle of a ring is 10cm, the diameter of the inner circle is 8cm, and the area is (28.26)cm2.
7. Bend a 12.56 decimeter iron wire into a circular iron ring (excluding the interface). iron hoop
Its diameter is (4) decimeter and its area is (12.56) square decimeter.
8. Complete the table below.
Radius r diameter d perimeter c area s of a circle.
4dm, 12.56dm, 12.56dm^2 2dm
6.28dm, 12.56dm,39.4384dm, 123.836576dm^2
8cm, 16cm,50.24cm,200.96cm^2
Second, discerning right from wrong.
1, the diameter is always greater than the radius. (Wrong, the same lap will do. )
2. The center of the circle determines the position of the circle, and the radius determines the size of the circle. (right)
The area of a circle is equal to the area of a square, and their perimeters must be equal. (error)
The circumference of a semicircle is half that of this circle. (error)
5. The diameter of the line segment with two ends on the circle is the largest. (right)
Third, sit in the right position.
1, the symmetry axis in the figure below is the most (b, circle).
A, square b, circle c, isosceles triangle
2. Minute length of the watch10cm. From 2 o'clock to 4 o'clock, the minute hand passed (b, 62.8) cm.
a、3 1.4 B、62.8 C、3 14
3. The circumference of a circle is 3 1.4 decimeter, and its area is (a, 78.5) square decimeter.
a、78.5 B、 15.7 C、3 14
4.Pi π(A, greater than) 3. 14.
A, greater than B, equals C, less than.
5. A semicircle with a radius of r and a circumference of (c, πr+2r.
)。
a、π4 B、πr C、πr + 2r
Fourthly, draw an axisymmetric figure of a given figure according to the axis of symmetry.
No charts
5. Calculate the area below. (Unit: cm)
No, uh, there are pictures.
6. You can solve this problem.
1. What is the width of this rectangle?
Lack of conditions
2. A flower bed, 5 meters in diameter, surrounded by a round cobblestone path, with a width of 1 meter.
How many square meters is the area of this path?
Path area = 3.14× (3.5× 3.5-2.5× 2.5) =18.84 m2.
Can you draw a circle with the largest area in the square on the right? If you cut off the largest circle, what is the remaining area?
Diameter of the largest circle = side length of a square.
The area of the rest = the area of the square-the area of the largest circle.
4. The bowling radius is about 1dm, and the fairway length is 18cm. How many times should bowling be rolled from one end to the other?
Is the fairway length 18cm or 18m?
Calculated by 18m.
At least rolling =18 ÷ (3.14× 0.1) = 57 cycles.
5. The shape of a piece of grass is the shaded part in the picture below. What is its circumference and area?
No charts
6. 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. With a range of 20m, 15m and 10m, which do you think is more suitable? Where is it installed?
The circumference is 62.8m, and the radius is 62.8/(3.14 * 2) =10m.
Choose the range of 10 meter, and install it in the center of the circular lawn.