All the answers of the seventh grade mathematics new observation people's education press in the next semester

All the answers of the seventh grade mathematics new observation people's education press in the next semester

It is recommended that you write a little bit every day, but you must first write the front and back, and finally write in the middle. If the holiday is over and you don't finish writing in the middle, you can write casually, so that you are beautiful at both ends!

Xiao Zhao and Xiao sun set out from place a to place B at the same time. Xiao Zhao's speed was 9km / h, and Xiao Sun's speed was 15km / h. Xiao Sun stopped on the way for 2 hours because of something, so he was 2 hours later than Xiao Zhao. He calculated the distance between two places

Suppose the distance between a and B is x km
The time of Xiaozhao is x / 9 hours
Xiaosun time = x / 15 + 2 hours
(X/15+2)-X/9=2/3
X/9-X/15=2-2/3
2X/45=4/3
X=30
The distance between a and B is 30 km

{2x+1/2y=7.（1）
{3x+2y=3.（2）

2x+1/2y=7.（1）
3x+2y=3.（2）
(1) * 4
8x+2y=28.(3)
(3) - (2) get
5x=25
x=5
Substituting x = 5 into (2) yields
y=-6
come on.

Find the trajectory equation of the moving point satisfying the following conditions: the distance from the X axis is equal to 2

y=2 or y=-2

Solving practical problems with linear equation of one variable
AB is 360km away from each other, car a is 72km / h, and car B is 48km / h. After 25 minutes, car B starts to walk, and the two cars continue to walk after meeting. When the distance between car a and car B is 100km, how long does it take for car a to walk?

2 km / min for car a 72 km / h and 0. 8 km / min for car B 48 km / h
The distance between a and B is 100km
(1.2+0.8)x=360+100-1.2×25
2x=430
x=215
A walked 215 minutes, a distance of 100km

What is the current land area in China?

According to the CIA of the United States, the land area is 9326410 square kilometers, and the water area is 270550 square kilometers. Other authoritative encyclopedias have also announced that China's land area is between 9.55-9.6 million

Newton's law of gravitation, right?

The fourth floor is wrong. It's not that it's not applicable in the micro level, but that the gravitational effect is covered by other forces in the micro level
F = GMM / R & sup2, g = (2 / 3) × 10 ^ (- 10) [nm & sup2 / kg & sup2], the mass of particles in the micro world is in the order of 10 ^ (- 27 ~ - 31) kg, and the distance is in the order of 10 ^ (- 14 ~ - 10) M. the gravitational force between particles is in the order of 10 ^ (- 44) n, which can be ignored compared with other electromagnetic forces, weak forces, strong forces, etc
Generally speaking, in three-dimensional space, the law of inverse square is applicable

There are five Sundays in February of a certain year, and the first of June of this year is Sunday______ ．

If there are only 28 days in February, there are only 4 Sundays, so it is easy to get that February is 29 days, and February 1 is Sunday, so is February 29. March 1 is week 1, and the interval between June 1 and March 1 is 31 + 30 + 31 = 92 days. So June 1 is week 2

A group of mowers should cut off two pieces of grass. The big one is twice as big as the small one. All the team members spend half a day cutting the big one first. In the afternoon, they split it in half, and half of them still stay on the big one. In the evening, they just finish cutting the big one, and the other half goes to the small one. In the evening, there is still a small piece left, which is cut by one person How many people are there in this group?

What is the remainder of the 70th division by 6?

The law of numbers is a (n + 1) = 3A (n) - A (n-1)
Number 70 is 1150043320
The remainder is four