The radius of a circle is equal to the side length of a square. The area of a square is 3 square decimeters. The area of this circle is 3 square decimeters

Area of a circle: π times the square of the radius. The radius is exactly the side length of the square. The square of the radius is the area of a square, which is 3 square decimeters. So 3 π square decimeters

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1. The sum of the circumference of the two circles is 78.5cm. The radius ratio of the big circle to the small circle is 3:2. What is the area of the big circle
2. If the radius of the big circle is twice that of the small circle, and the area of the big circle is 12 square centimeters more than that of the small circle, then the area of the small circle is () A. 12 square centimeter B. 4 square centimeter C. 6 square centimeter D. 8 square centimeter
3. The radius of a small circle is 3cm, and that of a large circle is 5cm. The simplest integer ratio of the area of a large circle to that of a small circle is______ ．
4. The radius of a small circle is 3cm, the radius of a large circle is 4.5cm. What is the simplest integer ratio of the circumference of a small circle to a large circle
5. The diameter of the small circle is 5cm, the radius of the big circle is 5cm, the perimeter ratio of the big circle and the small circle is (), and the area ratio is () Write down the formula
6. For a ring, the radius of the inner circle is 3cm, the radius of the outer circle is 5cm, and the area of the ring is () square cm
7. The radius of the outer circle of a ring is 7cm, and the radius of the inner circle is 5cm?
8. The radius of a ring is 5cm, the width of the ring is 1cm, and how many square centimeters is the area of the ring?
9. The radius of the outer circle of a ring is 5cm longer than that of the inner circle, and the radius of the inner circle is 3cm. What is the area of the ring?
10. A circular ring, the diameter of the outer circle is 5cm, the radius of the inner circle is 3cm, how many square meters is its area?
11. The side length of a square is equal to the radius of a circle, and the area of a square is 5 square decimeters (hint: a = R, the square of a = R, the square of a)
12. The radius of a circle is equal to the side length of a square. Given that the area of a square is 3 square decimeters, how many square decimeters is the area of the circle?
13. According to the requirements: as shown in the figure, the square area is 18dm2, find the area of the circle
14. 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
15. If the perimeter of the square in the figure is 4cm, then the area of the circle is______ Square decimeter (π = 3)
16. The perimeter of a circle and a square is equal. The area of a square is 5 square decimeters. What is the area of a circle? I need it this afternoon. Come on······
17. In the figure, the area of a square with the radius of the circle as the side length is 75 square centimeters
18. Two cuboids, 5cm long, 4cm wide and 3cm high, can be assembled______ A cuboid with different surface area, the smallest surface area is______ Square centimeter
19. A cuboid has the same width and height. If the length is removed by 2.5cm, it will become a square cuboid with a surface area of 150cm
20. The bottom surface of a cuboid is a square with a side length of 5cm, and its surface area is 210 square cm. Height? Not only requires process, but also text explanation. Thank you Not only the process, but also the text. Thank you. Not only the process, but also the text. Thank you