The area of a circle is 78.5cm. Find the circumference,

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• 1. There is a wall clock in the school hall. The length of the hour hand from the fixed point to the tip of the needle is 25cm, which is the same as how many centimeters the needle end of the hour hand walks day and night?
• 2. Cut off a rectangle 2cm wide from the square sheet, and the remaining area is 48cm2. Then the area of the original square sheet is () A. 9cm2B. 68cm2C. 8cm2D. 64cm2
• 3. Physics problems in grade two The total mass of an empty bottle filled with water is 700g. If 108G metal block is put into the empty bottle, the total mass is 768g 1. Volume of metal block 2. The density of this metal block You can't do it with buoyancy. I haven't learned it
• 4. The distance between the two feet of a compass is 5cm. If you draw a circle, what is the circumference of the circle______ What is the area of this circle______ ．
• 5. The maximum and minimum of sine function y = - 6sin (2X-4 π) + 1 Seeking process
• 6. Put a round scissors into a rectangle, increase the circumference by 8 cm, and find the circumference and area of the circle
• 7. If lgx = 3.1502, what is x equal to?
• 8. The side length of a square is equal to the diameter of a circle. It is known that the perimeter of the square is 20cm. How many square centimeters is the area of the square larger than that of the circle?
• 9. Let the population x obey the normal distribution x ~ n (μ, σ ^ 2), and x1, X2,..., xn be a sample from the population, Let u = [√ n (x - μ)] / σ, then d (U)=（
• 10. A rectangular conference room is 9 meters long and 8 meters wide. If you use square tiles with a side length of 2 decimeters, how many bricks do you need
• 11. A mathematics application problem is urgent! Xiao Liang's house painted the room and finished it after 10 days; he used 150 liters of certain paint, and the paint cost was 4800 yuan; the painting area was 130 square meters, and the final settlement of the payment was as follows: 1. According to the work, each worker was 30 yuan (one worker worked a day); 2. According to the paint cost, 30% of the paint cost was used as the payment; 3. According to the painting area, Pay 12 yuan per square meter. Which plan do you think is the most economical--
• 12. It is known that P is a point outside the parallelogram ABCD, the diagonal AC and BD intersect at O, and AP ⊥ CP
• 13. Let f (x) be continuous on [0, π], and be derivable within (0, π). It is proved that there exists ξ ∈ (0, π) such that f '(ξ) sin ξ + F (ξ) cos ξ = 0
• 14. Let f (x) be continuous on [0, π], and be derivable in (0, π). It is proved that there exists ξ ∈ (0, π) such that f '(ξ) sin ξ + 2F (ξ) cos ξ = 0
• 15. Let f (x) = (sin ^ 4 x-cos ^ 4 X-5) / (cos2x + 2); (a) prove that f (x) = 3 / (2 sin ^ 2 x-3) - 1 (b) find the range of F (x)
• 16. It is proved that ∫ (0, π / 2) (f SiN x / (f SiN x + F cos x) DX = π / 4
• 17. Let f (x) = cos X. prove that (COS x) '= - sin
• 18. Cos (x + 6 π) = 4 / 5 why sin (x + 6 π) = 3 / 5
• 19. If f (3sinx) = cos square X / sin square x is known, find f (x)= I'm a beginner. Please elaborate
• 20. Y = cos square x-sin square x + 3sinx Find the maximum and minimum