The passenger and freight cars leave from a and B at the same time. When they meet, the distance between them is 5:4. After the meeting, the freight car is 15 kilometers faster than the passenger car per hour, and the passenger car is still moving at the same speed. As a result, the two cars arrive at each other's departure station at the same time. It is known that when the freight car runs for 10 hours, there is a long distance between a and B

Bus speed: truck speed 4:5
Bus speed 15 △ 5-4 X4 = 60 km
The distance between the two places is 60x10 = 600km

Urgently seek the answer of four plane vector review reference question for mathematics compulsory course (people's Education Press)
1. Judge whether the following propositions are correct
→ →
(1)AB+ BA =0 ( )
→ → →
(2)AB+BC = AC ( )
→ → →
(3)AB- AC =BC ( )
→
(4)0AB=0 ( )
From here on, the answer of group A and group B should be the same

Yes, yes

There are two classes a and B, and the number of class a accounts for 5 / 8 of the two classes. After 9 people are transferred from Class A, the number ratio of class A and B is 2:3
Q: how many people were there in the two classes?

The original number of class a accounted for 5 / 8 of class B (1-5 / 8) = 5 / 3
Now class a accounts for 2 / 3 of class B
The number of class a decreased by 5 / 3-2 / 3 = 1
The number of class a decreased by 9
There are 9 people in class B
It turns out that there are 15 students in class A

How many natural numbers from 1 to 1000 do not contain 4 at all

This is equivalent to 729 of the 9-ary median less than 4

The whole journey from point a to point B is 760km. The bus starts from point a at the speed of 80km / h, and the car starts from point B at the speed of 120km / h,
Excuse me, when will the car meet the bus?

T = 760 ÷ (80 + 120) = 3.8 = 3.48
So we met at 13:48, 1:48 p.m
Don't know how to ask me

Angle 2 is three times of angle 1. How many degrees does angle 1 Equal? How many degrees does angle 2 equal? (the sum of the degrees is 180 degrees.)

1+3=4
∠1=180°÷4=45°
∠2=45°x3=135°
Answer: 1 = 45 ° and 2 = 135 °
I'm glad to solve the above problems for you. I hope it will be helpful to your study

After driving from Shanghai to Nanjing, the original plan was to arrive at 11:30 noon. But after starting, the speed increased by 17 and arrived at 11:00. The next day, I returned from Nanjing at the same time. After driving 120 kilometers according to the original plan, I increased the speed by 16 and arrived in Shanghai at 11:10. How many kilometers is the distance between the two places?

Suppose the original planned speed of the car is XKM, 11:30-11:00 = 30 minutes = 12 hours, 12 ^ [1 ^ (1 + 7)], = 12 ^ [1 ^ [8], = 12 ^ [18, = 4 (hours); 11:30-11:10 = 20 minutes = 13 hours & nbsp; 4x-120 = (4-120 ^ X-13) × (1 + 16) x, & nbsp; 4x-120 = (4-120x-13)

Sum: SN = 1 / (1 ^ 2 + 3) + 1 / (2 ^ 2 + 6) + 1 / (3 ^ 2 + 9) +. + 1 / (n ^ 2 + 3n)

1/(n^2+3n)=1/n(n+3)=[1/n-1/(n+3)]/3
Sn=1/(1^2+3)+1/(2^2+6)+1/(3^2+9)+.+1/(n^2+3n)
=[1-1/4+1/2-1/5+1/3-1/6+1/4-1/7+-----+1/(n-1)-1/(n+2)+1/n-1/(n+3)]/3
=[1+1/2+1/3-1/(n+1)-1/(n+2)-1/n+3)]
=11/6-(3n^2+12n+11)/(n^3+6n^2+11n+6)

The railway between a and B is 840 km long. A train leaves from a to B at 5:30 p.m. on the first day, with an average of 70 km per hour. When does the train arrive at B?

840 △ 70 = 12 (hours), 5:30 + 12 hours = 17:30, a: the train arrives at B at 17:30

Given a = 2x & sup2; + 3xy-2x-1, B = - X & sup2; + XY-1, if 3A + 6B has nothing to do with the value of X, try to find the value of Y

A = 2x & sup2; + 3xy-2x-1, B = - X & sup2; + xy-13a + 6B = 3 (2x & sup2; + 3xy-2x-1) + 6 (- X & sup2; + XY-1) = 6x & sup2; + 9xy-6x-3-6x & sup2; + 6xy-6 = 15xy-6x-9 = (15y-6) x-93a + 6B has nothing to do with the value of X, 15y-6 = 0y = 3 / 5

There are two classes a and B, and the number of class a accounts for 5 / 8 of the two classes. After 9 people are transferred from Class A, the number ratio of class A and B is 2:3 Q: how many people were there in the two classes?