If the perimeter of the square in the figure is 4cm, then the area of the circle is______ Square decimeter (π = 3)

4 △ 4 = 1 (centimeter) 1 △ 2 = 0.5 (centimeter) 3 × 0.52 = 0.75 (square centimeter) = 0.0075 (square decimeter) answer: the area of a circle is 0.0075 square decimeter, so the answer is: 0.0075

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1. 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
2. According to the requirements: as shown in the figure, the square area is 18dm2, find the area of the circle
3. 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?
4. 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)
5. 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
6. 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
7. 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
8. 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______ ．
9. 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
10. 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
11. 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······
12. In the figure, the area of a square with the radius of the circle as the side length is 75 square centimeters
13. 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
14. 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
15. 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
16. A cuboid is known as a square whose bottom side is 5cm long, and its surface area is 210cm square. Find its volume
17. What is the square of the surface area and the cube of the volume of a cuboid 10 cm long, 6 cm wide and 5 cm high?
18. If the edge length of a cube is a, the sum of its edge lengths is (); if a cuboid is 4.5cm in length, width and height, the sum of its edge lengths is () cm Use two cubes whose edges are 3cm long to form a cuboid. The surface area of the cuboid is (). Hurry!
19. It needs at least () cm long wire to make a rectangular frame with a bottom area of 16 square centimeters and a height of 5cm
20. A rectangle 5cm long and 6cm wide is 4:1 enlarged, and the area of the figure is () square centimeter