The circumference of a semicircle is 15.42 meters, and its radius is______ Rice

The circumference of a semicircle is 15.42 meters, and its radius is______ Rice

If the radius of the circle is r m, then 2 × 3.14r-14r r \r \14r-2 + 2 + 2R = 15.42-15.42 & amp & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & 3

It is known that the circumference of a semicircle is 15.42 decimeters, and the radius of the semicircle is several decimeters

2R+pai*R=(2+pai)R=5.14R=15.42
R = 3 decimeters

1. The circumference of a semicircle is 15.42dm, and the diameter of the semicircle is () decimeter
2. The outer radius of a ring is 12cm, the inner radius is 8cm, and the area of the ring is () square centimeter
3. Divide a circular piece of paper with a circumference of 6.28cm into several parts along its radius, and then cut it open to form an approximate rectangle with an area equal to that of the circle. The circumference of the rectangle is () cm
4. The perimeter ratio of two circles with radius of 2cm and 10cm is (), and the area ratio is ()

1. Radius: 15.42 △ 3.14 + 2 = 3 (CM)
So the diameter is: 3x2 = 6 (CM)
2. 3.14x (12x12-8x8) = 3.14x80 = 251.2 (cm2)
3. The radius of the circle is:
6.28÷(2x3.14)=1(cm)
The circumference of rectangle is: 6.28 + 1x2 = 8.28 (CM)
4. Perimeter ratio: 1:5, area ratio: 1:25

The circumference of a semicircle is 30,84 decimeters, and the area is?

Radius = 30.84 ÷ (3.14 + 2) = 6dm
Area = 6 × 6 × 3.14 × 1 / 2 = 56.52 square decimeter