Put the circle together into an approximate rectangle. The length of the rectangle is 6.28 decimeters. The area of the circle is______ Square centimeter, perimeter is______ Decimeter

Put the circle together into an approximate rectangle. The length of the rectangle is 6.28 decimeters. The area of the circle is______ Square centimeter, perimeter is______ Decimeter

The circumference of the circle: 6.28 × 2 = 12.56 (decimeter); the area of the circle: 3.14 × (12.56 △ 3.14 △ 2) 2 = 3.14 × 4, = 12.56 (square decimeter). Answer: the area of the circle is 12.56 square decimeter, the circumference is 12.56 decimeter. So the answer is: 12.56, 12.56

After dividing a circle into several equal parts, it forms an approximate rectangle. The circumference is increased by 4 decimeters

4 △ 2 = 2 (decimeter) 3.14 × 22 = 3.14 × 4 = 12.56 (square decimeter)

After dividing a circle into several equal parts, it can be put together into a rectangle with a circumference of 20.7 decimeters. How many square decimeters is the area of this circle?

Let the radius of a circle be r, 3.14 × 2R + 2R = 20.7, & nbsp; & nbsp; 6.28r + 2R = 20.7, & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; 8.28r = 20.7, & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; r = 2.5, and the area of the circle be 3.14 × 2.52 = 19.625

For square and circle with equal perimeter, the ratio of side length to radius is______ ：______ The area ratio is______ ：______ ．

The ratio of side length to radius is: C4 ／ C2 π = C4 × 2 π C = π 2, the ratio of area is: (C4) 2 ／ [π × (C2 π) 2] = c216 ／ [π × C24 π 2] = c216 ／ C24 π = c216 × 4 π C2 = π 4, answer: the ratio of side length to radius is π: 2, the ratio of area is π: 4