In Cartesian coordinate system, a point whose distance from the coordinate axis to the point (6, - 8) is equal to 10 is common

In Cartesian coordinate system, a point whose distance from the coordinate axis to the point (6, - 8) is equal to 10 is common

Three (X-6) ^ 2 + (y + 8) ^ 2 = 100, x = 0 and y = 0 get (0,0) (0, - 10) (10,0)

（x²+y²）²-4x²y²

(x²+y²)²-4x²y²=(x²+y²)²-(2xy)²=[(x²+y²)+2xy][(x²+y²)-2xy]=(x²+2xy+y²)(x²-2xy+y²)=(x+y)²(x-y)²

What is the country with the largest area of cultivated land in the world?

The top five cultivated areas in the world are: America, India, Canada, China and Russia

The charged ball a with a mass of 0.2g is hoisted with a wire. If the ball B with a charge of 4 * 10 is close to him, when the two balls are 3cm apart at the same height, the angle between the wire and the vertical is 45 degrees. At this time, the Coulomb force received by the ball B is f =?
The charge quantity of the ball a QA =?

Why can the silk thread form a 45 ° angle with the vertical direction? What is the state of the ball at this time? According to the conditions given, we can know that the ball a is in a state of equilibrium, and analyze the force on the ball A. mg: the gravity of the ball A. ft: the tension of the silk thread. F: the electrostatic force of the ball B on the ball a. the resultant force of the three forces is zero
F＝mgtan 45°＝0.2×10^－3×10×1 N＝2×10^－3 N.
In the question, balls a and B are regarded as point charges, they attract each other, and the force F = K
F＝k＝mgtan 45°,
So QA = C = 5 × 10 ^ - 9 C

According to the first page of the calendar, calculate the day of the week on the next two pages of the calendar
August 8, 2008 is Friday
What day is August 8, 2009?

365/7=52 …… one
August 8, 2008 is Friday
August 8, 2009 is Saturday

Chemical expression of grade three (character + symbol + phenomenon)!
I need it urgently. Thank you
I want a literal expression, such as red phosphorus + oxygen → = phosphorus pentoxide (conditional ignition on the arrow)

Chemical reaction
Combustion of magnesium in air: 2mg + O2 ignites 2MgO
Combustion of iron in oxygen: 3Fe + 2O2 ignites Fe3O4
Combustion of aluminum in air: 4Al + 3O2 ignites 2al2o3
Combustion of hydrogen in air: 2h2 + O2 ignites 2H2O
Combustion of red phosphorus in air: 4P + 5o2 ignites 2p2o5
Sulfur powder burning in air: S + O2 ignites SO2
Full combustion of carbon in oxygen: C + O2 ignites CO2
Incomplete combustion of carbon in oxygen: 2C + O2 ignites 2CO
Carbon dioxide passing through hot carbon layer: C + CO2 high temperature 2CO
Combustion of carbon monoxide in oxygen: 2CO + O2 ignites 2co2
Reaction of carbon dioxide and water (carbon dioxide into purple litmus test solution): CO2 + H2O = = H2CO3
Combustion of sodium in chlorine: 2Na + Cl2 ignites 2nacl
decomposition reaction
Preparation of oxygen from hydrogen peroxide in laboratory: 2h2o2, MnO2, 2H2O + O2 ↑
Heating potassium permanganate: 2kmno4 △ k2mno4 + MnO2 + O2 ↑
Heating potassium chlorate (with a small amount of manganese dioxide): 2kclo3 MnO2 2KCL + 3O2 ↑
Under the action of direct current, water is electrified by 2H2O, 2h2 ↑ + O2 ↑
The carbonic acid is unstable and separated into H2CO3 = = = H2O + CO2 ↑
High temperature calcined limestone (carbon dioxide industrial process): CaCO3 high temperature CaO + CO2 ↑ industrial preparation of carbon dioxide and quicklime
Displacement reaction
Reaction of iron with copper sulfate solution: Fe + CuSO4 = = FeSO4 + Cu
Reaction of zinc with dilute sulfuric acid (hydrogen production in laboratory): Zn + H2SO4 = = ZnSO4 + H2 ↑
Reaction of magnesium with dilute hydrochloric acid: Mg + 2HCl = = = MgCl2 + H2 ↑
Reduction of CuO by hydrogen: H2 + CuO △ Cu + H2O
Reduction of CuO by charcoal: C + 2CuO, high temperature 2Cu + CO2 ↑
Water vapor passing through the hot carbon layer: H2O + C, high temperature H2 + CO
Reduction of iron oxide by coke: 3C + 2fe2o3, high temperature 4Fe + 3co2 ↑
other
Methane combustion in air: CH4 + 2O2 ignites CO2 + 2H2O
Alcohol burning in air: C2H5OH + 3O2 ignites 2co2 + 3H2O
Reduction of copper oxide by carbon monoxide: CO + CuO △ Cu + CO2
Reduction of iron oxide by carbon monoxide: 3Co + Fe2O3 high temperature 2Fe + 3co2
Carbon dioxide passes through clarified lime water (test carbon dioxide): Ca (OH) 2 + CO2 = = CaCO3 ↓ + H2O
Reaction of sodium hydroxide with carbon dioxide (removal of carbon dioxide): 2naoh + CO2 = = Na2CO3 + H2O
Reaction of limestone (or marble) with dilute hydrochloric acid (laboratory preparation of carbon dioxide)
CaCO3 + 2HCl === CaCl2 + H2O + CO2↑
1、 Reaction of substance with oxygen:
(1) Reaction of elemental matter with oxygen: there are
(2) Reaction of compound with oxygen:
Combustion of carbon monoxide in oxygen: 2CO + O2 ignites 2co2 blue flame and gas burns
Methane combustion in air: CH4 + 2O2 ignites the blue flame of CO2 + 2H2O, exothermic, methane and natural gas combustion
Alcohol burning in air: C2H5OH + 3O2 ignites 2co2 + 3H2O blue flame
2、 There are several redox reactions
Reduction of CuO by hydrogen: H2 + CuO △ Cu + H2O
Reduction of CuO by charcoal: C + 2CuO, high temperature 2Cu + CO2 ↑
Reduction of iron oxide by coke: 3C + 2fe2o3, high temperature 4Fe + 3co2 ↑
Reduction of Fe3O4 by coke: 2C + Fe3O4 high temperature 3Fe + 2co2 ↑
Reduction of copper oxide by carbon monoxide: CO + CuO △ Cu + CO2
Reduction of iron oxide by carbon monoxide: 3Co + Fe2O3 high temperature 2Fe + 3co2
Reduction of Fe3O4 by carbon monoxide: 4Co + Fe3O4 high temperature 3Fe + 4co2
3、 The relationship among element, oxide, acid, alkali and salt
Zinc and dilute sulfuric acid Zn + H2SO4 = ZnSO4 + H2 ↑
Iron and dilute sulfuric acid Fe + H2SO4 = FeSO4 + H2 ↑
Magnesium and dilute sulfuric acid Mg + H2SO4 = MgSO4 + H2 ↑
Aluminum and dilute sulfuric acid 2Al + 3h2so4 = Al2 (SO4) 3 + 3h2 ↑
Zinc and dilute hydrochloric acid Zn + 2HCl = = = ZnCl2 + H2 ↑
Iron and dilute hydrochloric acid Fe + 2HCl = = = FeCl2 + H2 ↑
Magnesium and dilute hydrochloric acid Mg + 2HCl = = = MgCl2 + H2 ↑
Aluminum and dilute hydrochloric acid 2Al + 6hcl = = 2alcl3 + 3h2 ↑
Reaction of marble with dilute hydrochloric acid: CaCO3 + 2HCl = = = CaCl2 + H2O + CO2 ↑
Sodium carbonate reacts with dilute hydrochloric acid: Na2CO3 + 2HCl = = = 2nacl + H2O + CO2 ↑
4、 Other reactions:
Quicklime dissolved in water: Cao + H2O = = = Ca (OH) 2
5、 Application of chemical equation reaction phenomenon
2mg + O2 ignites 2mg O and burns violently. It produces white solid, exothermic and white signal bomb
The experiment of 2hg + O2 igniting 2hgo silver white liquid to produce red solid lavasside
2Cu + O2 ignites 2CuO red metal and turns into black solid
4Al + 3O2 ignites 2al2o3 silver white metal and turns into white solid
3Fe + 2O2 ignites Fe3O4 to burn violently, sparks radiate, black solid is formed and exothermic
C + O2 ignites CO2 to burn violently, white light, release heat, and make lime water turbid
S + O2 ignites SO 2 intense combustion, exothermic, pungent gas, light blue flame in air and blue purple flame in oxygen
2h2 + O2 ignites 2H2O light blue flame, exothermic and high energy fuel
4P + 5o2 ignites 2p2o5, which burns violently, gives off a lot of white smoke, and produces white solid, which proves the oxygen content in the air
2kclo3, MnO2, 2KCL + 3O2 ↑ to produce the gas for the reburning of wood strips with Mars
2kmno4 △ k2mno4 + MnO2 + O2 ↑ turns purple to black, and generates the gas that makes the wood with Mars reburning. Oxygen is prepared in the laboratory
The experimental results show that 2hgo △ 2hg + O2 ↑ red changes to silver white and produces the gas which makes the wood with Mars reburning
2H2O power on 2h2 ↑ + O2 ↑ father is itching
Fe2O3 + 3h2 △ 2Fe + 3H2O red gradually turns to silvery white, the wall of test tube has liquid smelting metal and reducibility of hydrogen
One of the common reactions, air pollutants and gas poisoning in ignition of 2CO coal furnace by 2C + O2
C + CuO high temperature 2Cu + CO2 ↑ black gradually turns red, produces the gas which makes the clarified lime water turbid, and smelts metal
CuO + CO △ Cu + CO2 black gradually turns red, and produces the gas which makes clear lime water turbid to smelt metal
CO2 + H2O = H2CO3, the litmus turned red by carbonic acid, which proved the acidity of carbonic acid
H2CO3 △ CO2 ↑ + H2O litmus red fading
Ca (OH) 2 + CO2 = CaCO3 ↓ + H2O clear lime water becomes turbid apply CO2 test and lime slurry to paint the wall
CaCO3 + 2HCl = CaCl2 + H2O + CO2 ↑ the solid dissolves gradually and has the gas which makes the clarified lime water turbid. The carbon dioxide is prepared and the scale is removed in the laboratory
Fe + CuSO4 = Cu + FeSO4 the silver white metal surface is covered with a layer of red substance
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
1. Combustion of magnesium in air: 2mg + O2 ignites 2MgO
2. Combustion of iron in oxygen: 3Fe + 2O2 ignites Fe3O4
3. Copper heated in air: 2Cu + O2 heated 2CuO
4. Combustion of aluminum in air: 4Al + 3O2 ignites 2al2o3
5. Combustion in hydrogen and air: 2h2 + O2 ignites 2H2O
6. Combustion of red phosphorus in air: 4P + 5o2 ignites 2p2o5
7. Sulfur powder burning in air: S + O2 ignites SO2
8. Full combustion of carbon in oxygen: C + O2 ignites CO2
9. Incomplete combustion of carbon in oxygen: 2C + O2 ignites 2CO
10. Combustion of carbon monoxide in oxygen: 2CO + O2 ignites 2co2
11. Methane combustion in air: CH4 + 2O2 ignites CO2 + 2H