It takes 8 hours for a bus to go from station a to station B, and 12 hours for a train to go from station B to station A. two trains leave from two stations at the same time, How many kilometers is the distance between station a and station B?

It takes 8 hours for a bus to go from station a to station B, and 12 hours for a train to go from station B to station A. two trains leave from two stations at the same time, How many kilometers is the distance between station a and station B?

When they met, the bus traveled 39 * 2 = 78 km more than the train (the bus was 39 km more than half the distance, and the train was 39 km less than half the distance)
Speed ratio of passenger train to train = 1 / 8:1 / 12 = 3:2
When meeting, the distance ratio is 3:2 (the whole distance is divided into 5 parts), 3 / 5 buses, 2 / 5 trains, 3 / 5-2 / 5 buses, 1 / 5 trains
The distance between station a and station B is 78 / (1 / 5) = 390km

If a is a rational number, the reciprocal of a can be expressed as a / 1

It does not hold when a = 0

If the speed of light in vacuum is C = 3 × 10 ^ 8m / s, when the velocity of an object is V1 = 2.4 × 10 ^ 8m / s, the mass is 3kg, and when its velocity is V2 = 1.8 × 10 ^ m / s, what is the mass?

m=m0/√(1-v²/c²)
m1/m2 = √(1-v2²/c²) / √(1-v1²/c²)
m2 = √(1-v1²/c²) m1/√(1-v2²/c²) = √(1-0.8²)/√(1-0.6²) ·3 = 2.25(kg)

The solution of equation 5x-2a = 2x + 1 is x = 2, and the value of a is obtained

a=5/2
Substituting x = 2 into
We get 10-2a = 4 + 1
2a=5
a=5/2

According to the book of physics, in practice, the maximum static friction is slightly greater than the sliding friction. For the sake of simple calculation, it can be considered that the maximum static friction is approximately equal to the sliding friction
So why is the maximum static friction slightly greater than the sliding friction?
That is to say, when a pulling force just pulls an object, the force is greater than the force pulling it forward at a constant speed?
The maximum static friction is a limit. When the force reaches this limit, the object will slide and become sliding friction?

This is proved by experiments. It is very difficult in theory. It may be that the essence of elastic force and friction force is that the object is squeezed, which disturbs the arrangement order of atoms in the object. As a result, the distance between atoms changes, which leads to the change of inter atomic force (that is, electromagnetic force). In appearance, they are elastic force and friction force

How to solve the linear equation of one variable X-13 * 3-x-16 * 2 = 6
Sorry, I didn't make it clear. I want to say that 12 percent x multiplied by 3 minus 16 percent x multiplied by 2 equals 6

If I understand correctly, X / 13 * 3 means 3x / 13?
Both sides of the equation are multiplied by 13 * 16 to get:
16*x*3-13*x*2=16*13*6
48x-26x = 1248
So x = 1248 / (48-26) = 1248 / 22 = 624 / 11
If the building owner's X / 13 * 3 means 3 * 13 / x
Then the two sides of the equation are multiplied by X to get:
13*3-16*2=6x
That is 39-32 = 6x
So x = 7 / 6

It takes 8 hours for a ship to go back and forth between port a and B. from a to B, it is 45km per hour, and return is 35km per hour. How many kilometers is the distance between port a and B?
Please write the process reason?

45:35 = 9:7 speed ratio
7: 9 time ratio
8 × 7 / (7 + 9) = 3.5 hours from a to B
3.5 × 45 = 157.5km AB distance

a^2(a+1)-b^2(b+1)

=(a^3-b^3)+(a^2-b^2)
=(a-b)(a^2+ab+b^2)+(a-b)(a+b)
=(a-b)(a^2+ab+b^2+a+b)

A simple calculation of 999 times 3 / 998

999 times 3 / 998
=（998+1）* 3/998
=3+3/998
=3 and 3 / 998

The total weight of the three steel plates is 207kg. The weight of the first steel plate is three times that of the second steel plate, and the weight of the second steel plate is two times that of the third steel plate. How many kg do the three steel plates weigh?

1 + 2 + 6 = 9, weight of the third block: 207 △ 9 = 23 (tons), weight of the second block: 23 × 2 = 46 (tons), weight of the first block: 46 × 3 = 138 (tons); answer: weight of the first block: 138 tons, weight of the second block: 46 tons, weight of the third block: 23 tons