If S10 = 10, S30 = 20, then S20=

Isn't the answer right
S10=10
S20=32/5
that
The S30 will be smaller than the S20
S30/3=S20-S10
S20=50/3

If {an} is known to be an arithmetic sequence, A2 + A8 = 12, then A5=______ ．

∵ {an} is an arithmetic sequence, A2, A5, a8 are an arithmetic sequence, and A2 + A8 = 12, ∵ 2a5 = A2 + A8 = 12, ∵ A5 = 6

What is the meaning of the two ways of expression: how much is the current working and how much is the transformed electric energy?

Work done by current: w = uit, meaning the consumed electric energy
If you want to say that the only way to convert into electric energy is the power supply, that is how much electric energy is generated!

My life composition is 800 words

There is science everywhere in our life, but we just don't pay attention to it. People can't live without science anywhere in their daily life. As for production, labor, sports, health and military affairs, science is even more needed. "Being proud of science and ashamed of ignorance" spreads a lot of common sense in our daily life, which are the experience of our predecessors, We mechanically think that these common sense of life are correct and beneficial, and often do it without thinking. As time goes by, it makes your life troublesome, because these so-called "experience" and "common sense" are just contrary to the common sense of life. To believe in science, only by respecting science can you avoid taboos and be less troubled by it
In winter, when the weather is cold, the glass bottle cap can't be unscrewed, and it can't work with any force. An experienced person can easily unscrewing the bottle cap just by baking it on the fire. Do you know why? This is the truth of heat expansion and cold contraction, So it doesn't take much effort to open it
When the old man wears a needle hard, she puts it on her hair and rubs it. Do you know why? It's actually lubrication to reduce friction. Human hair contains grease. When the needle rubs her hair, it is equal to adding lubricating oil. Therefore, friction can be reduced and the needle can be easily pierced
Lunch meat, mud carp with lobster sauce, beans with tomato sauce They are all delicious canned food. They can be stored for a long time without deterioration. Because canned food is sealed, bacteria can't enter. When people make canned food, they take out all the air in the can and then seal it, They also can't survive or reproduce! This makes use of the air in the living conditions of microorganisms
Some foods can not be heated with high temperature, otherwise their nutrition and taste will be affected. For these foods, we can quickly heat them to a certain temperature (generally 60 ℃ ~ 85 ℃) for 15 to 30 minutes, and then quickly cool them down. This can kill most of the microorganisms in the food and keep the original taste. This heating method is called pasteurization, It was invented by French scientist Louis Pasteur,
Science needs to study all kinds of natural phenomena and find out the causes and laws of their emergence and development. Every little doubt may lead to scientific discovery. Lsaac Newton was curious about the apple landing and discovered the law of everything; James Watt was curious about the boiling water and raised the lid of the kettle and improved the steam engine, We can all enter the world of science. Science is around us

If ∠ 1 and ∠ 2 are equal to 90 degrees, ∠ 3 and ∠ 2 are equal to 90 degrees, and ∠ 1 is equal to 40 degrees, then ∠ 3 is equal to 90 degrees

1 plus 2 equals 90 degrees
1 equals 40 degrees
Then ∠ 2 = 50 degrees
If ∠ 3 plus ∠ 2 is equal to 90 degrees
∠ 3 = 90-50 = 40 degrees
If ∠ 3 minus ∠ 2 equals 90 degrees
∠ 3 = ∠ 2 + 90 degree = 90 + 50 = 140 degree

How to simplify the operation of half plus two thirds plus two ninths

1/2+2/3+2/9
=9/18+12/18+4/18
=25/18;
If you don't understand this question, you can ask,

The resistance R1 of lamp Li is 1 / 2 of the resistance R2 of lamp L2. The power supply voltage is 10V and remains unchanged. S1 and S2 are switches,
The lamp L1 lights normally, the electric power consumed by the resistor R3 is 2W, and the indication of the voltmeter is UI
When S2 is closed and S1 is opened, the electric power consumed by resistor R4 is 1 / 4W, and the indication of voltmeter is 1 / 2ui
Calculate (1) rated power of lamp L1. (2) resistance of R4

It's easy to get the result by calculating according to the formula in the book

After a particle moves eastward at a speed of 3 M / s for 3 s, it immediately moves westward at a speed of 2 m / s for 2 s. try to draw a V-T image and calculate its displacement within 5 s. (take the East as the positive direction)

Take the East as the positive direction, drive eastward at the speed of 3m / s for 3S, and then drive westward at the speed of 2m / s for 2S immediately. The image is as shown in the figure. The area enclosed by the image and t axis is the displacement within 5S, s = 3 × 3m-2 × 2m = 5m, and the direction is eastward. A: V-T as shown in the figure, the displacement within 5S is 5m, and the direction is eastward

In the international system of units, the unit of speed is determined by Unit and Its basic unit is Read as The symbol is Or ．

Speed is the physical quantity that indicates the speed of an object's movement. It refers to the distance that an object passes in unit time. The formula is: v = St. the distance belongs to length. In the international system of units, the unit of distance of length is meter, and the unit of time is second. Therefore, the unit of speed is meter / second, read as meter / second, and the symbol is m / s s-1．

One end of a light spring is fixed, and the other end is tied with a small ball with a mass of M. at the same time, a light rope is used to connect the small ball with a mass of M
Cut the string first, then at the moment of cutting the string
(1) What are the accelerations and directions of a and B balls?
(g = 9.8m per second)

For B, let the elastic force of the rope be n, n = mg before cutting; after cutting, n is zero, only under the action of gravity, so the acceleration is g = 9.8, and the direction is vertical and downward
For a, it is balanced before cutting. If the spring force is f, the force balance is f = Mg + n = 2mg;
At the moment after cutting, n is zero and the spring force is constant, so the force is uneven, f = f-mg = mg; acceleration a = f / M = g, the direction is vertical and upward

If S10 = 10, S30 = 20, then S20=