In this paper, the equation 2x-7y = 4 is transformed into an algebraic expression with X, and the form of Y is

In this paper, the equation 2x-7y = 4 is transformed into an algebraic expression with X, and the form of Y is

y=(2x-4)/7
Maths 2x + 3y-z = 11 2x + y-5z = 8 - 2x + 7Y + Z = 19 equations
2x+3y-z=11 …… （1）
2x+y-5z=8 …… （2）
-2x+7y+z=19 …… （3）
（1）-（2）：
2y+4z＝3 …… （4）
（2）+（3）：
8y-4z＝27 …… （5）
（4）+（5）：
10y＝30
So y = 3
We substitute y = 3
2×3+4z＝3
therefore
z＝－3/4
therefore
x＝11/8
Solution: 2x + 3y-z = 11
2x+y-5z=8 ②
2x+7y+z=19③
① Y = 3
Substituting y = 3 into (1) and (2) gives 2x-z = 2 (4), 2x-5z = 5 (5)
④ (5) get z = - 3 / 4
Substituting y = 3, z = - 3 / 4 into (1) yields x = 11 / 8
So x = 11 / 8, y = 3, z = - 3 / 4
2x+3y-z=11 ①
2x+y-5z=8 ②
-2x+7y+z=19 ③
①+③：
10y=30
Y=3
Substitute:
2x+9-z=11,
2x-z=2 ④
2x+3-5z=8,
2x-5z=5 ⑤
④ - ⑤：
-6z=-3
z=0.5
Substitute:
2x-2.5=5
2x=7.5
x=3.75
According to the meaning of the title
2x+3y-z=11 ①
2x+y-5z=8 ②
-2x+7y+z=19③
① Y = 3
Substituting y = 3 into (1) and (2) yields
2x-z=2④
2x-5z=5⑤
④ (5) get z = - 3 / 4
Substituting y = 3, z = - 3 / 4 into (1) yields
x=11/8
So x = 11 / 8
Y=3
z=-3/4
In May 2007, a primary school in Kaixian County of Chongqing was struck by lightning, which caused many casualties. If the energy of a certain lightning is 4 × 109J, the power released by this lightning can supply 100W light bulbs to work continuously______ If the duration of the lightning is 0.1s, its power is______ W．
When the bulb works continuously, t = WP = 4 × 109j100w = 4 × 107s, the power of lightning P1 = WT1 = 4 × 109j0.1s = 4 × 1010w
Every 1kvar low-voltage capacitor can save 0.09 × 24 hours = 2.16kwh power per day
What is 0.09
New discovery: work done by inductor load in parallel with proper capacitor increases [original]
Although it is not clear whether capacitor can be used to save power or not in the book
I have discussed this problem for more than 30 years. Through the analysis of the signal selection ability of the tuning circuit, I found the reason why the capacitor is used to save electric energy: the main reason is the use of the circuit resonance phenomenon, which can be called "generalized circuit resonance"
With the help of leaders and comrades, many experiments have been carried out to prove whether the use of capacitors can save electric energy, especially the news about energy saving. I found that the work done by inductor load in parallel with proper capacitors increases
1、 Practice is the only criterion for testing truth
The fact of using capacitor to save electric energy is undeniable. The essence of saving and increasing is the same. If the amount of work done by the load is constant, the input electric energy is reduced, which is called saving electric energy; if the amount of work done by the load is constant, which is called increasing energy
When installing appropriate capacitors in the power system, the input electric energy is reduced due to the same amount of work done by the load, which is called saving electric energy. In order to prove whether the use of capacitors can save electric energy, the input energy and output energy are changing, it is necessary to compare the input electric energy and load work done by the power supply before and after the installation of capacitors
The test results are as follows:
1. In my experiment:
(1) Test equipment and circuit: ① in front of the 100 volt transformer, connect a 220 volt 60W electric bulb (not shown in the figure) to separate and connect with the main circuit. ② connect a suitable capacitor in parallel at the input end of the transformer. ③ connect a 20W bulb at the output end of the transformer, as shown in the figure
(2) Test methods: ① setting the capacitor to the minimum capacity position is like breaking the circuit. At this time, the bulb is not very bright after connecting the bulb. The primary current measured by the ammeter is 0.32 a, and the secondary current is 0.5 a
② Adjust the capacity of the capacitor to a proper position, that is, the capacitive reactance is equal to the inductive reactance. It is found that the light bulb is brighter than before. Measure the primary current 0.25 A and the secondary current 0.6 a again
(3) The results show that: (1) the input current decreases: (0.32-0.25) △ 0.32 = 21%;
② The output current increases: (0.6-0.5) △ 0.5 = 20%,
③ Because there is no power meter, it is impossible to measure whether the input active power decreases or not, but the input electric energy will not increase due to the decrease of current. However, the output is a pure resistance load, the active power factor is 1, the current increases, the voltage can not be reduced, and the output active power increases by more than 20%. This test is not required to measure, It is proved that the capacitor not only saves a lot of active power, but also increases the load work
2. The test of steel wire plant of Dalian Steel Works: according to the report of No.253 of iron and steel information in 1994, the plant installed capacitors on 154kw asynchronous motors. The trial operation proved that the power factor was 0.1 ~ 0.15 higher than the original, and the power failure was less. According to the calculation of power consumption, the annual reduction was 15%. According to the statistics in the first half of 1994, after using this power saving technology, the actual power saving was 32000 kwh, and the benefit was 16000 yuan
According to this energy-saving effect, if the capacitor is installed on the 500kW asynchronous motor, the annual electricity saving is 100000 yuan. Medium sized enterprises can have 10 ~ 20 such motors. If the capacitor is fully installed, the annual electricity saving is 1 ~ 2 million yuan
3. Qidashan Iron Mine of Angang mining company;
According to the report of Anshan Iron and steel daily on April 26, 1995, the unit has installed all 19 Electric shovels with capacitance compensators successively, resulting in a power saving rate of 18% and an annual power saving of 38000 kwh for each shovel. If the unit is calculated at 0.4 yuan per kWh, it can save 282800 yuan per year for 19 Electric shovels
According to the unit: after the installation of the capacitor, the voltage is stable, and the problem of starting difficulty is solved. In the past, it took more than two minutes to start, and the rated speed was reached in less than one minute after the installation of the capacitor
4. Experiment (letter) of netizens:
I haven't done such an experiment before. I did it today. The experiment process is as follows: the first experiment:
There is no change of output current and voltage after shunt capacitor
Analysis: our power grid is in good condition, the internal resistance is very small, and the transformer power is not very large
The second experiment: a resistor is connected in series in front of the transformer to simulate the power grid with large internal resistance
Among them, R1 = 1K Ω, R2 = 1 Ω, C = 0.5 μ M
（1） Before shunt capacitor:
The primary current is 0.08A, the voltage is 160V, the apparent power is about 12.8w, and the active power is 8.1w
The output current is 2.75a, the voltage is 2.75V, and the power is about 7.56w
（2） After shunt capacitor: ×
The primary current is 0.06a, the voltage is 174v, the input current of transformer is 0.087 a, the apparent power is about 15.138w, the active power is 9.6w, the active power factor is 0.6328, the active power rate plus: 9.6-8.1 = 1.5W
(0.087×174-0.08 ×160)×0.6328=(15.138-12.8)×0.6328=1.479W
The output current is 2.97a, the voltage is 2.97v, and the power is about 8.82w
The primary apparent power decreases by 72.5% and the active power increases by 18.5%
The output power is increased by 16.7%
The above four tests show that: the inductor load parallel with appropriate capacitor can not only compensate the loss of reactive power, but also increase the active power by about 20%. It is a new discovery that the capacitor can increase the active power while compensating the reactive power
2、 The calculation of surgical formula is the best way to explain the problem
1. It is generally accepted that the current in the load is greater than the total input current
In AC circuit, the acting force is the power supply (voltage) and the reaction force is the load (impedance). The amount of work done by the power supply (for electrons) is directly proportional to the voltage and inversely proportional to the total impedance. The calculation formula: I = u / Z; when the circuit is resonant, the calculation formula: q = x / R; I negative = Qi total impedance
It is generally accepted that the current in the inductive load is greater than the total input current
2. The calculation formula of active power increase in inductive load is consistent with the fact
The input power of generator and transformer is determined by the output power. In the transformer or motor, the inductive reactance and impedance are constant, and the active power factor is also constant
It is known from practice that when the parallel circuit resonates, the inductive load has high impedance characteristics. In fact, the terminal voltage of the load increases and the current increases. This phenomenon is not mentioned in the electrical book, and it is an objective fact (see the small test above for details). This is a new discovery
Because the active power factor of inductive load (transformer or motor) remains unchanged, for inductive load: P = iucos φ, as cos φ remains unchanged, I and u increase, P will inevitably increase. Calculation formula: Section P = (i2u2-i1u1) cos φ; where I2 and U2 represent the current and voltage in load after installing capacitor; I1 and U1 represent the current and voltage before installing capacitor
In the book of electrical engineering, the formula for calculating the cost of energy saving is: P section = (i21-i22) r. when the resistance in the circuit is very small, there is little power saving. Especially in the case of inductive load, there is no formula for calculating the power saving. It is mistakenly believed that the magnitude of current and voltage in the load does not change, and the magnitude of load work does not change. In the total circuit, the input current decreases, and the active power factor increases, So many people think that the installation of capacitors is good for the power sector and bad for the unit
3. Parallel resonant circuit has the characteristic of high impedance, which is the result of internal electromotive force
The current in the inductive load is the sum of the current vector in the total circuit and the current vector in the capacitive branch. The current in the inductive load is directly proportional to the terminal voltage and inversely proportional to the impedance in the load. Because the total impedance value in the load remains unchanged and the terminal voltage increases, the current in the load increases. This phenomenon is like two batteries in parallel in a DC circuit
Both the book and the experts admit that the installation of appropriate capacitors in the power system can stabilize the voltage, and the voltage and current are inseparable. In the formula I = u / Z, I represents the current, u represents the voltage, and Z represents the total impedance
3、 The significance of the new discovery
The new point of view is the new development of the theory in the book, and there is no contradiction with the calculation formula in the book. It is difficult for people to understand why the circuit resonance produces energy, so we will not talk about this problem for the time being. We will only talk about the practical significance and scientific value of the load work increase after the shunt capacitor
1. Practical significance: it can explain the reason of using capacitor to save electricity, and has great benefits to promote the use of capacitor to save electricity
2. Scientific value: when the increased active power of circuit resonance is greater than the copper loss, the electric energy can be expanded. Example: when the quality factor Q is greater than 2, the current in the load is 2 times of the total input current, and the active power in the load is 2 times of the original
It is known from the test results of netizens that the output active power of the shunt capacitor is 8.82, and the input active power will not increase compared with that before installation, which is 8.1; the increase is: (8.82-8.1) △ 8.1 = 8.8%; because the output is greater than the input, it is proved that the energy is generated when the circuit resonates
(1) From the small test results, we know that once compensation can save 10-20% of electricity, and then remove all kinds of losses, it can also save about 10%, if continuous compensation will continue to expand the power
(2) In the past, people only compensated reactive power in inductive load, but not in pure resistive load
(3) The resonance energy can be increased by increasing the current frequency. Because the inductance is proportional to the current frequency, the quality factor can be improved by increasing the frequency. The quality factor is an important parameter of resonance energy
(4) Explosive inventions: many great inventions can be made by using the new theory. The "resonant energy generator" can be used in cars, trains, ships, power stations and other places to solve the problem of energy shortage and promote the great development of productivity
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