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What is the minimum number? It includes natural number, negative number, decimal number, etc
Negative infinity
A way in which a negative value represents infinitesimal. There is no specific number, but negative infinity represents a value smaller than any number. The sign is - ∞
Or not
The extension of number system and the introduction of complex number
Given that the complex z = x + Yi (x, y ∈ R, X ≥ 1) is full of Z-2 = x, the trajectory equation of the corresponding point of Z in the complex plane is obtained
The complex number corresponding to Z-2 is X-2 + Yi, and the square of his formula is (X-2) ^ 2 + y ^ 2 = x ^ 2
So y ^ 2 = 4x-4
Why the plural?
In the wave part, the complex form is used to replace the form of functional equation. Why? It is said in the book for convenience. Where is it convenient? I think the main reason is that the square of I is negative 1, but what's the advantage of this? Can you make it more popular?
The introduction of complex number is of great significance
1. The complex plane composed of real axis and imaginary axis introduces the concept of number from one dimension to two dimensions
2. Introduce the concept of direction, which is more important in physics, because some physical quantities are not only size, but also direction (such as force, velocity, current, voltage analysis, etc.)
3. The knowledge of complex number is applied to many problems, such as series in mathematics, Euler formula, some differential equations, solution of motion equation of spring oscillator in physics, atomic structure, energy level and so on
Without plural, there would be no modern science, so to speak
Simple calculation of 1 / 3 + (0.75 + 0.25 / 2 / 3)
What letters (symbols) are used to express quantities in chemistry?
For example, the amount and mass fraction of solubility substances
What are "n" and "C"?
Solubility s mass fraction of substance n mass fraction of substance w mass concentration C molar mass m
Mass m volume V density P molar volume VM Avogadro constant Na
Simple calculation of 38.5 minus 5.38 plus 61.5 minus 4.62
38.5 minus 5.38 plus 61.5 minus 4.62
=（38.5+61.5）-（5.38+4.62）
=100-10
=90
In the circuit shown in the figure, the range of ammeter is 0 ~ 0.6A, and that of voltmeter is 0 ~ 3V. The sliding rheostat is marked with "50 Ω 1A". When the switch S is closed and the slide of sliding rheostat slides to a certain position, the indication of ammeter is 0.3A, and that of voltmeter is 3V; when the slide of sliding rheostat slides to another position, the indication of ammeter is 0.5A, and that of voltmeter is 3V The indication is 1V. Calculate: (1) the resistance value and power supply voltage of resistor R1; (2) to ensure the safety of the circuit, adjust the range of sliding rheostat R2
(1) Switch S is closed, when the current number I1 = 0.3A, voltage number U1 = 3V, power supply voltage U = i1r1 + U1 = 0.3A × R1 + 3V ① When I2 = 0.5A, U2 = 1V, u = i2r1 + U2 = 0.5A × R1 + 1V ② The solution of the two equations is u = 6V, R1 = 10 Ω. (2) in order to ensure the safety of the ammeter, the maximum current in the circuit is I1 = 0.6A, so the minimum resistance R2 = ui1 − R1 = 6v0.6a − 10 Ω = 0 Ω ③ In order to ensure the safety of the voltmeter, the maximum voltage at both ends of the rheostat is u ′ R2 = 3V, so the voltage at both ends of the resistor R1 is ur1 = u − u ′ R2 = 6V − 3V = 3V, so the maximum resistance of the rheostat is R ′ 2 = u ′ r2ur1r1 = 3v3v10 Ω = 10 Ω ④ The adjustable range of the rheostat should be controlled between 0 Ω and 10 Ω. Answer: (1) the resistance value of the resistor R1 is 10 Ω, and the power supply voltage is 6V; (2) to ensure the safety of the circuit, the adjustable range of the sliding rheostat R2 is 0 Ω to 10 Ω
Mathematical real number calculation
Radical 12 - radical & #189; - 2 * one third of the radical
The original formula is √ 12 - √ (1 / 2) - 2 * √ (1 / 3) √ 12 = 2 √ 3 √ (1 / 2) = {2 / 2 √ (1 / 3) = {3 / 3} 12 - 2 * √ (1 / 3) = 2 √ 3 - 2 √ 3 / 3 = 4 √ 3 / 3 -------- (1) original formula = (1) formula - √ (1 / 2) = (1) formula - √ 2 / 2 = 8 √ 3 / 6 - 3 √ 2 / 6
How do you type this sign
Remove the input method and press the key "enter" directly, next to enter
I found the beauty in life
There must be a specific case. About 420 words
"Beauty" contains many meanings. It is very simple to say, but to understand it, one person may have different views. There is such a small matter that I have witnessed with my own eyes, and I understand it in this way Listen to me!
One morning in the summer vacation, the weather was hot and the streets were busy with pedestrians. As usual, I went to the sunshine composition class to learn composition. Just as I was walking along the West Cross Road, I found such a pair of "mother and son", and my sight was attracted by them. I found that the old lady was gray haired, and she was walking in the middle of the road alone, It looks very dangerous. Suddenly, a 20-year-old brother rushed forward from the opposite side to help his grandmother cross the road carefully. The grandmother gave him a faint smile. The elder brother didn't say anything and waved to the old man with a knowing smile. This scene is like the normal care between a mother and a child. The pedestrians on the roadside are still in such a hurry, As if nothing had happened. This is what I caught in the eyes of a 12-year-old girl. At this time, I stood there staring, this scene has not happened in front of my eyes for a long time. "Di, di..." The sound of the car woke me up. When I looked back, the taxis were all in a long line. When I crossed the road and looked back for the "mother and son", the old lady had already gone far alone. Such a small thing made me understand a lot in a flash
The Beijing Olympic Games will soon be held in our country. At that time, people from many countries in the world will come to our country to participate in competitions or sightseeing. Our country has 5000 years of ancient civilization and has an excellent tradition of respecting the old and caring for the young. How I hope that such a small thing can happen every day, although it is trivial and insipid, Although we can't win honor for our motherland in the Olympic Games, we can do more to help others, which is also a kind of support for the Beijing Olympic Games. This is not only sweet to others, but also sweet to ourselves
Beauty is everywhere. For our eyes, it is not the lack of beauty, but the lack of discovery. For ourselves, we should do more good deeds and help the people in need. How beautiful the world should be!
And now, I found beauty, not only with my eyes, but also with my heart!
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