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A batch of saplings will be planted. If each person plants 10 saplings, the remaining 6 saplings will not be planted. If each person plants 12 saplings, the remaining 6 saplings will be missing. How many people plant trees? List the equations according to the meaning of the question
With X race
10X+6=12X-6
X=6
The distance between a and B is 42 km. Xiaoming starts from a to B by bike at the speed of 20 km / h. 0 and 4 hours later, Xiaogang starts from B by motorcycle. 0.5 hours later, they meet on the way,
The answer to this question is 48 km / h
We need a specific explanation, thank you
20 * 0.4 = 8km Xiaoming's 0.4 hour ride
42-8 = 34km, which is the rest of Xiaoming's journey after riding for 0.4 hours
Let the minimum rigid speed be x km / h
0.5（x+20）=34
The solution is x = 48
Xiaogang's speed is 48 km / h
Pure hand fight for the best
1. Party A and Party B set out from AB and went towards each other. When they met, Party A walked 6 kilometers more than Party B. after meeting, they still went at the same speed. Party A arrived at place B after 4.5 hours, and Party B arrived at place a after 8 hours
Ask the speed of a and B
2. Train a and B start from ab which is 450 km away from each other at the same time. After meeting each other, they still go at the same speed. After 4.5 hours, train a arrives at place B, and train B arrives at place a after 2 hours, so as to find the speed of train a and B
3. The area difference between the two squares is 5 square centimeters. The area of the right triangle formed by taking the length of the two squares as the right side is 3 square centimeters. Find the length of the middle line on the third side of the right triangle
I want the right formula or equations! Make one or two
First floor pro, can you think about question 2 or 3 again, and I can give it to you.
1.
Let a speed x km / h and B speed y km / h
8y-4.5x=6
4.5x/y=8y/x
y=(6+4.5x)/8
8y^2=4.5x^2
8[(6+4.5x)/8]^2=4.5x^2
(6+4.5x)^2/8=4.5x^2
6^2+54x+20.25x^2=36x^2
15.75x^2-54x-36=0
63x^2-216x-144=0
(7x+4)(9x-36)=0
X = 4 or x = - 4 / 7
y=(6+4.5x)/8=(6+4.5*4)/8=3
A: the speed of a is 4 kilometers per hour, and that of B is 3 kilometers per hour
two
Let a be x km / h and B be y km / h
4.5x+2y=450
4.5x/y=2y/x
y=(450-4.5x)/2
2y^2=4.5x^2
(450-4.5x)^2/2=4.5x^2
450^2-450*9x+20.25x^2=9x^2
11.25x^2-4050x+202500=0
The results are as follows
9x^2-3240x+162000=0
The solution is as follows
X = 60 or x = 300
When x = 60, y = (450-4.5 × 60) / 2 = 90
When x = 300, Yb > 0
a^2-b^2=5………… （1）
ab=3×2=6
b=6/a
Substituting (1), we get:
a^2-(6/a)^2=5
a^2-36/a^2=5
Let m = a ^ 2, m ≥ 0, then:
m-36/m=5
m^2-5m-36=0
(m-9)(m+4)=0
M = 9 or M = - 4 (rounding off)
therefore
a^2=9
a=3
b=6/a=6/3=2
The median line on the third side is equal to half of the length of the third side
√ (a ^ 2 + B ^ 2) / 2 = √ (3 ^ 2 + 2 ^ 2) / 2 = (√ 13) / 2 (13 under the root of 2)
Chemical characters and symbolic expressions in the first semester of junior three
Please help me to find, as long as last semester,
Oxygen o hydrogen h nitrogen n potassium K Si Pb ne Na Au Ag
Fluorine, magnesium, magnesium, calcium, copper, copper, zinc and zinc
As long as the
It's like this
light
Red phosphorus + oxygen ----- → phosphorus pentoxide
light
There are only 11 P + O2 --- → p2q5
Red phosphorus + oxygen ignition phosphorus pentoxide
P + O2 -- Ignition -- p2q5
Sulfur + oxygen ignition sulfur dioxide
S + O2 -- Ignition -- SO2
Iron + oxygen ignition Fe3O4
Fe + O2 -- Ignition -- Fe3O4
Hydrogen peroxide -- manganese dioxide -- water + oxygen
H2O2--MnO2--H2O+O2
Potassium chlorate -- manganese dioxide and heating -- Potassium Chloride + oxygen
KClO3 -- MnO2 and heating -- KCl + O2
Potassium permanganate -- Heating -- Potassium Permanganate + manganese dioxide + oxygen
KMnO4 -- Heating -- k2mno4 + MnO2 + O2
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
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
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 ↑
Words and chemical symbol expressions are needed to solve several chemical formulas
1. Add copper sulfate solution into sodium carbonate solution
Sodium oxychloride
Copper chloride decomposes when heated
Reaction of oxygen with 4 red phosphorus sulfur charcoal iron wire
1.Na2Co3+CuSo4____ Na2SO4 + cuco3 (precipitation)
In fact, copper carbonate does not exist in water, because the degree of hydrolysis of copper carbonate is very large. Copper hydroxide and water are produced by hydrolysis, and copper carbonate can also combine with copper hydroxide to form basic copper carbonate. Therefore, copper carbonate does not exist in solution, but exists in the form of copper hydroxide and a small amount of basic copper carbonate. Therefore, the solution is blue with a small amount of green precipitation
2. What to add? I don't understand
3.2 CuCl2 ==△== 2 CuCl + Cl2
4.4p + 5o2 = △ = = 2p2o5 red phosphorus combustion
S + O2 = = △ = = SO2 sulfur combustion
C + O2 = = △ = = CO2, sufficient combustion of carbon
2C + O2 = = △ = = co carbon insufficient combustion
3Fe + 2O2 = △ = = Fe3O4 iron burns in oxygen
Watchtower master, change the second question, otherwise you really can't do it!
What is the meaning of triangle in chemical literal expression
The chemical expression can not be expressed by △ but must be written with the word "heating". In the process of writing chemical equation, the reaction is carried out under the condition of heating, and then it can be expressed by "△"
What is the expression of methane combustion symbol?
fifty
What is the symbolic expression of methane combustion?
CH4 + 2O2 (ignition) = CO2 + 2H2O
Chemical symbol expression of hydrogen combustion?
2h2 + O2 = = 2h20 (= ignition above)
Symbolic expression of magnesium combustion in oxygen
Symbolic and literal expressions
2mg + O2 = 2MgO condition: ignition
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