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Given C = 25.12 cm, find the area of this circle
C is the circumference of a circle. If you want to find out the area of a circle, you need to know the radius. Therefore, we can deduce it from the circumference (25.12). Because the circumference of a circle = radius × 2 × 3.41, the radius is equal to 25.12 △ 3.14 △ 2 = 4 (CM). If you know that the radius is 4cm, you can find the area of a circle: 3.14 × 4 & sup2; = 50.24 (CM & sup2;)
A: the area of this circle is 50.24 square centimeters
The area of the big circle is 112.5% of that of the small circle, and the area of the big circle is ()% more than that of the small circle
The area of large circle is 112.5% of that of small circle
The area of a small circle is unit 1
If the area of the big circle is larger than that of the small circle, use (112.5% - 100%) / 1
That is to say, the area of the big circle is more than that of the small circle (). Unit 1 is still a small circle
So the answer is 12.5% more
The radius of small circle and big circle are 2 cm and 5 cm respectively. The area ratio of small circle and big circle is ()
A. 2：5B. 4：10C. 4：25D. 2：10
The area of the small circle is: π × 22 = 4 π, the area of the big circle is: π × 52 = 25 π, the ratio of the area of the small circle to the area of the big circle is: 4 π: 25 π = 4:25, so choose: C
With 16 yuan, I bought 28 stamps of 40 Fen, 60 Fen and 80 Fen. The total price of 40 Fen stamps is the same as that of 60 Fen stamps. How many stamps did I buy?
List the equations,
Here's what I listed: let's set the score of 40, 60 and 80 and buy x, y and Z pieces respectively,
x+y+z=28
40x+60y+80z=1600
40x=60y
For. X + y + Z = 28, ① 40x + 60y + 80z = 1600, ② 40x = 60y, ③ ① * 80, we get 80x + 80y + 80z = 2240, ④ - ②, we get 40x + 20Y = 640, namely 2x + y = 32, ⑤, we get 4Y = 32 from ③ 40x-60y = 0, namely 2x-3y = 0, ⑥, ⑤ - ⑥, so y = 8, y = 8, x = 12, y = 8, x = 12, z = 8, so x = 12, and y = 8
The trajectory equation of the point with the square difference of the distance between O (0,0), a (C, 0) and the earth constant C is obtained
Set the point as (x, y)
x^2+y^2-[(x-c)^2+y^2]=c
2cx-c^2=c
X = (c + 1) / 2, which is a linear equation
It is known that a is a root of the quadratic equation x2-5x + 1 = 0, and the value of A2 + 1A2 is obtained
Substituting x = a into the equation: a2-5a + 1 = 0, that is, a + 1A = 5, the square of both sides is: (a + 1a) 2 = A2 + 1A2 + 2 = 25, then A2 + 1A2 = 23
What does the comparison of steel and electricity production between China and India and the United States show
I'm talking about falling behind
In 2009, China's crude steel output was 567.8 million tons, accounting for 47% of global crude steel output; India's crude steel output was 56.6 million tons; and the United States' crude steel output was 58.1 million tons. In 2009, China's installed power generation capacity was 874000 MW; India's 147000 MW; and the United States's about 1.1 million MW
On the horizontal plane of smooth insulation, there are two small balls with the same charge, which are close to each other. If they are released from rest, the distance between the two balls ()
A. When the distance increases, the Coulomb force increases B. when the distance decreases, the Coulomb force increases C. when the distance increases, the Coulomb force decreases D. when the distance decreases, the Coulomb force decreases
According to the Coulomb's law, the Coulomb force between two spheres with the same charge is f = kqqr2, Q and Q remain unchanged, R increases, f decreases
Today is Wednesday, March 6, 2013. Can you figure out the last day of this month? What day is the 31st?
Do you want arithmetic or common answers
In arithmetic, 31-6 = 25 (days) 25 / 7 = 3 more than 4 weeks, and then count 4 days later, that is Sunday
Another way is to check the number, which is also Sunday
Junior high school requirements for all chemical equations and text expressions!
Chemical reaction equation
Chemical reaction
1. Combustion of magnesium in air: 2mg + O2 ignites 2MgO
2. Combustion of iron in oxygen: 3Fe + 2O2 ignites Fe3O4
3. Combustion of aluminum in air: 4Al + 3O2 ignites 2al2o3
4. Combustion of hydrogen in air: 2h2 + O2 ignites 2H2O
5. Combustion of red phosphorus in air: 4P + 5o2 ignites 2p2o5
6. Sulfur powder burning in air: S + O2 ignites SO2
7. Full combustion of carbon in oxygen: C + O2 ignites CO2
8. Incomplete combustion of carbon in oxygen: 2C + O2 ignites 2CO
9. Carbon dioxide passing through hot carbon layer: C + CO2 high temperature 2CO
10. Combustion of carbon monoxide in oxygen: 2CO + O2 ignites 2co2
11. Reaction of carbon dioxide and water (carbon dioxide into purple litmus test solution): CO2 + H2O = = = H2CO3
12. Quicklime dissolved in water: Cao + H2O = = = Ca (OH) 2
13. Anhydrous copper sulfate as desiccant: CuSO4 + 5H2O = = = = CuSO4 &; 5H2O
14. Combustion of sodium in chlorine: 2Na + Cl2 ignites 2nacl
decomposition reaction
15. Preparation of oxygen from hydrogen peroxide in laboratory: 2h2o2, MnO2, 2H2O + O2 ↑
16. Heating potassium permanganate: 2kmno4 heating k2mno4 + MnO2 + O2 ↑
17. Under the action of direct current, water is electrified by 2H2O, 2h2 ↑ + O2 ↑
18. The carbonic acid is unstable and separated into H2CO3 = = = H2O + CO2 ↑
19. High temperature calcined limestone (carbon dioxide industrial process): CaCO3 high temperature CaO + CO2 ↑
Displacement reaction
20. Reaction of iron with copper sulfate solution: Fe + CuSO4 = = FeSO4 + Cu
21. Reaction of zinc with dilute sulfuric acid (hydrogen production in laboratory): Zn + H2SO4 = = ZnSO4 + H2 ↑
22. Reaction of magnesium with dilute hydrochloric acid: Mg + 2HCl = = = MgCl2 + H2 ↑
23. Reduction of copper oxide by hydrogen: H2 + CuO heating Cu + H2O
24. Reduction of CuO by charcoal: C + 2CuO, high temperature 2Cu + CO2 ↑
25. Methane burning in air: CH4 + 2O2 ignites CO2 + 2H2O
26. Water vapor passes through the hot carbon layer: H2O + C, high temperature H2 + Co
27. Coke reduced iron oxide: 3C + 2fe2o3, high temperature 4Fe + 3co2 ↑
other
28. Reaction of sodium hydroxide solution with copper sulfate solution: 2naoh + CuSO4 = = Cu (OH) 2 ↓ + Na2SO4
29. Methane burning in air: CH4 + 2O2 ignites CO2 + 2H2O
30. Alcohol burning in air: C2H5OH + 3O2 ignites 2co2 + 3H2O
31. Reduction of copper oxide by carbon monoxide: CO + CuO heating Cu + CO2
32. Carbon monoxide reduced iron oxide: 3Co + Fe2O3, high temperature 2Fe + 3co2
33. Carbon dioxide: Ca (OH) 2 + CO2 = = = = CaCO3 ↓ + H2O
34. Reaction of sodium hydroxide with carbon dioxide (removal of carbon dioxide): 2naoh + CO2 = = = = Na2CO3 + H2O
35. Reaction of limestone (or marble) with dilute hydrochloric acid (laboratory preparation of carbon dioxide): CaCO3 + 2HCl = = = CaCl2 + H2O + CO2 ↑
36, sodium carbonate and concentrated hydrochloric acid reaction (foam extinguisher principle): Na2CO3 + 2HCl = = = 2NaCl + H2O + CO2
RELATED INFORMATIONS
- 1. The radius of the big circle is equal to the diameter of the small circle. The sum of the areas of the two circles is 100 square centimeters. The area of the big circle is 100 square centimeters______ Square centimeter
- 2. How to calculate the area of a circle
- 3. Static friction and sliding friction Isn't the maximum static friction the horizontal thrust of an object at the moment when it is about to move? Then the friction becomes smaller when the object gets up? Besides, doesn't sliding friction require the object to move relatively? If the thrust of the object is less than sliding friction, how does it move, A thing weighs 500N, the maximum static friction is 300N, and u is 0.56. One asks how much force is given to keep it moving at a constant speed when it moves, and how much sliding friction is given to push it 200N until it stops? The answers are all 280n. What's the matter? 200N is smaller than 280n. How does it move?
- 4. How to measure static friction and sliding and rolling friction? Calculation formula So under what circumstances is the force acting on an object equal to static friction?
- 5. How many forces does an object bear when it is placed on an inclined plane? I wrote about gravity, support force and static friction force. I want to ask if I wrote more or less
- 6. How to calculate the work done by an object on an inclined plane? What is the formula?
- 7. As shown in the picture, a and B measure the distance from the river bank to the cliff. Standing on the bank, a is 20m away from B. they stand on a straight line from the river bank to the cliff. A fires a shot, B hears two shots, and the interval between the two shots is 4S. Calculate the distance from the river bank to the cliff. (set the sound propagation speed as 340 & nbsp; m / s)
- 8. In the formula of sliding friction f = μ n, can μ be greater than 1?
- 9. Does static friction do work or not depends on the selected reference frame?
- 10. The direction of static friction on an object may be perpendicular to the direction of motion of the object. Who can explain? It's best to give an example
- 11. What is the formula for finding the radius of a circle Given that the area of a circle is π (8a) (M2), find its radius
- 12. How to find the radius of a circle? We need a formula
- 13. How to find the formula of midpoint and radius in the equation of circle x ^ 2 + y ^ 2 + DX + ex = k X ^ 2 + y ^ 2 + DX + ex = k, how to find the formula of the center and radius of a circle
- 14. If the equation of a circle is x ^ 2 y ^ 2-4y = 0, then the coordinate of the center of the circle is? What is the radius r? How to substitute it into the formula,
- 15. A formula for calculating circular equation It is some simple formulas, for example: know the coordinates of the two intersection points of the circle and the diameter, can directly solve the formula of the circle equation, and so on
- 16. Passing through the circle x ^ 2 + y ^ 2 = R ^ 2 (r > 0), a point P (x0, Y0) outside the circle is taken as two tangent lines of the circle, and the tangent points are m and N respectively. It is proved that the equation of the straight line Mn is x0x + y0y = R ^ 2
- 17. A number is 0.15 greater than 2% of 18.5. What is the number? Use the equation to solve
- 18. Gravity potential energy E = MGH, unit: for example, how to see the installed capacity of hydropower? How to budget the daily power generation?
- 19. The formula 1 / 2mV ^ 2 = MGH is suitable for the experimental conditions
- 20. Can the kinetic energy formula EK = MAS be derived from the gravitational potential energy formula EP = MGH? The value of gravitational potential energy calculated by gravitational potential energy formula is equal to the kinetic energy of the object at the moment of contact with the ground when it falls to the ground at that height Since kinetic energy is scalar, can we use acceleration a instead of acceleration g and distance s instead of height h to get EK = MAS? If an object moves horizontally, the initial velocity is known to be zero, the mass, the distance, and the kinetic energy of the velocity is calculated. Isn't this the same as doing a free falling body vertically? In this way, some problems can be solved, such as the initial velocity is zero, the mass is 0.2kg, the acceleration is 5mgs square, and the kinetic energy after 20m can be calculated. In this way, EK can be calculated directly without using the kinematic formula So, is EK = MAS equivalent to EK = 1 / 2 MV ^ 2? Can it be used as a kinetic energy formula? Thank you very much