Several real math problems in the first year of junior high school 1. Given that X and y are real numbers, and (x - √ 3) & sup2; and | y + 3 | are opposite numbers, try to find the value of X-Y (the result can retain the root sign) 2. It is known that the decimal part of √ 15 is a and the decimal part of √ 15 is B. try to find the value of a + B 3. There is such a question: "find the value of X that makes the equation x · √ x-2009 = 0 tenable." If x · √ x-2009 = 0, then x = 0 or √ x-2009 = 0, that is, x = 0 or x = 2009. Therefore, when x = 0 or x = 2009, the original formula holds Do you think sloppy's answer is correct? If not, please write the correct answer Can you write down the process of solving the problem? thank you! ~

Several real math problems in the first year of junior high school 1. Given that X and y are real numbers, and (x - √ 3) & sup2; and | y + 3 | are opposite numbers, try to find the value of X-Y (the result can retain the root sign) 2. It is known that the decimal part of √ 15 is a and the decimal part of √ 15 is B. try to find the value of a + B 3. There is such a question: "find the value of X that makes the equation x · √ x-2009 = 0 tenable." If x · √ x-2009 = 0, then x = 0 or √ x-2009 = 0, that is, x = 0 or x = 2009. Therefore, when x = 0 or x = 2009, the original formula holds Do you think sloppy's answer is correct? If not, please write the correct answer Can you write down the process of solving the problem? thank you! ~

1. Because (x - √ 3) & sup2; and | y + 3 | are opposite to each other, and because the value of (x - √ 3) & sup2; is greater than or equal to 0 | y + 3 | is greater than or equal to 0, so (x - √ 3) & sup2; = 0, | y + 3 | = 0, so x = √ 3, y = - 3
X-Y=√3+3
2. In the second question, you can calculate the integral part of √ 15 with a calculator
Then a = √ 15-3
B=-√15+3
A+B=√15-3-√15+3
A+B=0
3. No, the root can't be 0, so it's wrong
X = 2009 is not right, because it becomes 2009 · √ 2009-2009 is not equal to 0
So it's not right
√X-2009=0
So √ x = 2009
X=2009^2
(Note: are you missing brackets? Is it x · (√ x-2009) = 0? Otherwise, what I did is wrong.)

1. Which of the following approximate numbers are rounded to? How many significant numbers are there?
(1) 39.64 (2) 0079 (3) 720 million (4) 3.10 * 10 and 179;
2. In the following questions, to which exact are the approximate numbers? How many significant numbers are there?
1. China's population is about 1.3 billion
2. The output value of a factory in 2006 was about 85 million yuan, about 6.8 times that before 1998

1: (1) 39.64 accurate to percentile, with four significant digits; (2) 0.0079 accurate to ten thousand, with two significant digits; (3) 720 million accurate to one million, with three significant digits; (4) 3.10 * 10 square accurate to ten, with three significant digits
2: (1) 1.3 billion to 100 million; there are two significant figures;
(2) 85 million, accurate to 10000 digits, has four significant numbers

On the operation of real numbers in Mathematics
Addition, subtraction, multiplication and division is the first thing that we began to learn. However, the human use of addition, subtraction, multiplication and division is only a tool to measure quantity and days. But with the progress of science and technology, why can this kind of operation still be used in all aspects? Is the operation of real number a man-made rule or something that already exists

It seems that the building owner is very philosophical. In fact, this is a philosophical problem. Pythagoras, the discoverer of Pythagorean theorem, once proposed that number is the origin of all things, especially the number "1", because all numbers can be generated by its addition and subtraction. Of course, this is definitely wrong
Mathematics, as a natural science, is based on people's understanding of the world and summing up the world, so you will also find many physical theorems. If you have to go to the bottom of why it is gravitation rather than repulsion, then I think you can learn philosophy. Maybe you can give the world an answer. Come on
I hope I can help you

One variable equation
In 2011, after 9 rounds of the CSL, Guangzhou Evergrande ranked 19 points with an unbeaten result. According to the rules, how many games did the pair win, three points to win, one point to draw, one point to lose and one point to zero

If we win x field and draw y field, then
3x+y=19
And X + y ≤ 9,
When x = 1, y = 16
When x = 2, y = 13
When x = 3, y = 10
When x = 4, y = 7
When x = 5, y = 4 holds
When x = 6, y = 1 holds. At this time, we won 6 games, drew 1 game and lost 2 games
When x ≥ 7, it is impossible,
To sum up: there are two situations, 5-4 or 6-1-2

Chemical reaction equation of ethylene combustion in oxygen

C2H4+3O2=2CO2+2H2O

Ask: all chemical reaction equations about s in high school?

S + O2 = SO2 (concentrated) = 3so2 ↑ + 2H2O
S + 6hno3 (concentrated) = H2SO4 + 6no2 ↑ + 2H2O
S+4H++6==6NO2↑+2H2O+
3S + 4hno3 (dilute) = 3so2 + 4NO ↑ + 2H2O
3S+4H++4HNO3 = 3SO2+4NO↑+2H2O
Cl2+Na2S===2NaCl+S↓ \x05\x05\x05Cl2+S2–=2Cl–+S↓
Cl2 + H2S = = 2HCl + S ^ (in aqueous solution: Cl2 + H2S = 2H + + 2Cl – + S ^)
Cl2+SO2+2H2O===H2SO4+2HCl \x05\x05
Cl2+SO2+2H2O=4H++SO42–+2Cl–
S+H2 H2S \x05\x05\x052S+C CS2 \x05\x05\x05S+Zn ZnS
S + Fe FES
S + 2Cu Cu2S
3S + 2Al Al2S3 (can only be made from simple substance, not from ion)

High school chemical reaction equation!
The more the better! The more detailed the better!

1. Sodium carbonate and a small amount of hydrochloric acid
Na2CO3+HCl=NaCl+NaHCO3
2. Sodium carbonate and excessive hydrochloric acid
Na2CO3+2HCl==CO2↑ +H2O+2NaCl
3. Add a small amount of sodium hydroxide to the sodium bicarbonate solution
NaOH+NaHCO3=Na2CO3+H2O
4. Add excess sodium hydroxide to the sodium bicarbonate solution
NaOH+NaHCO3=Na2CO3+H2O
5. Reaction of aluminum with hydrochloric acid
2Al+6HCl=2AlCl3+3H2 ↑
6. Alumina and hydrochloric acid
Al2O3 + 6HCl = 2AlCl3 + 3H2O
7. Alumina and sodium hydroxide
Al2O3 + 2NaOH = 2NaAlO2 + H2O
8. Aluminum hydroxide and hydrochloric acid
Al(OH)3+3HCl=AlCl3+3H2O
9. Aluminum hydroxide and sodium hydroxide solution
Al(OH)3+NaOH=NaAlO2+2H2O
10. Aluminum chloride solution and excess ammonia water
AlCl3+3NH3·H2O=Al(OH)3↓+3NH4Cl
11. Add excess sodium hydroxide to aluminum chloride solution
AlCl3+3NaOH=3NaCl+Al(OH)3
Al(OH)3+NaOH=NaAlO2+2H2O
12. Add excessive hydrochloric acid into sodium metaaluminate solution
NaAlO2+4HCL=NaCL+AlCl3+2H2O
13. Magnesium burns in air
2Mg+O2＝2MgO
3Mg+N2=Mg3N2
2mg + CO2 = = = ignition = = = 2MgO + C
14. Iron and hydrochloric acid
Fe+2HCl=FeCl2+H2↑
15. Iron oxide dissolves in hydrochloric acid
Fe2O3+6HCl=====2FeCl3+3H2O
16. Drop sodium hydroxide into ferric chloride solution
FeCl3 + 3NaOH =Fe(OH)3↓+ 3NaCl
17. Iron burns in oxygen
3Fe + 2O2 = (ignited) Fe3O4
18. Add chlorine water to the ferrous solution
Cl2+2FeCl2=2FeCl3
19. Add iron powder to ferric chloride solution
Fe + 2FeCl3 =3FeCl2
20. Reaction of ferric chloride solution with copper
Cu+2FeCl3=CuCl2+FeCl2
21. Production of limestone from carbon
C+O2=CO2
CO2+CaO=CaCO3
22. Industrial bleach
2Cl2＋2Ca(OH)2＝CaCl2＋Ca(ClO)2＋H2O
23. Reaction of bleach solution with carbon dioxide
Ca(ClO)2+CO2+H2O=CaCO3↓+ 2HClO
The chemical equation is not simple
You should understand the principle, remember the writing rules of chemical equations, and understand the changes of chemical valence in the equations
And just remember some characteristic equations
Come on

In junior high school, there are basically four basic reactions, i.e. metathesis and so on. In senior high school, we will learn many reactions that do not belong to the four basic reaction types. Are these chemical equations written regularly? Do they all depend on memorization?
If there are rules, please be sure to make clear all the rules. I will spare no effort to teach me the rules, and I will not lose you

It seems that some of the above are copied from various websites. Here are some methods summarized by ourselves. I don't know whether they are suitable or not. In terms of organic, it's important to pay attention to the changes of various groups. For example, in methylbenzene, alkyl (methyl) and phenyl can affect each other

Can you provide all the chemical reaction equations in middle school?

The combustion of magnesium in air: 2mg + O2 ignites 2MgO 2, iron in oxygen: 3Fe + 2O2 ignites fe3o43, aluminum in air: 4Al + 3O2 ignites 2al2o34, hydrogen in air: 2h2 + O2 ignites 2h2o5, red phosphorus in air: 4P + 5o2

Summary of the writing standard of chemical reaction equation in Senior High School
I don't need to sum up the equations, I just need to write them
For example: thermochemical reaction equation does not write reaction conditions
The organic equation uses an arrow instead of an equal sign
The discharge equation of the negative electrode is precipitation, and the number of precipitation is not written
What I have mastered is messy, so I want to summarize
In addition, ask the electrode total reaction equation. If the product has precipitation and the reactant has no solid, then write the precipitation number (not for monopole)

The number of atoms on both sides of the chemical equation is the same. Don't forget to write the equal sign. The gas precipitation is accompanied by an arrow. In organic reactions, the arrow should replace the equal sign. The electrode reaction should indicate the state of existence of the substance