As shown in the figure, in the triangle ABC, point D is the midpoint of BC, de ⊥ AB, DF ⊥ AC, the perpendicular feet are e, F, be = CF ① How many pairs of congruent triangles are there? Please list them one by one ② Choose a pair of congruent triangles to prove Please forgive me if you draw any pictures!

① How many pairs of congruent triangles are there? Please list them one by one
For 3 pairs, △ ade is all equal to △ ADF △ bed is all equal to △ CFD △ ADB is all equal to △ ADC
② Choose a pair of congruent triangles to prove
All △ bed is equal to △ CFD
In △ bed and △ CFD
BD=CD
∠BED=∠CFD
BE=CF
（H.L.）
So △ bed is equal to △ CFD

How to say 2:30 in English

1.half past two
2.two thirty

Why does the earth revolve around the sun
Why can the earth revolve around the sun
Lei Shaowu, Leshan, Sichuan
If the earth can revolve around the sun, the distance from the sun is the key
The inertial force of the earth is possessed before it enters the solar system. Only when the earth's origin body enters the gravitational plane of the sun, its distance from the sun is different, there will be three completely different phenomena
One is to assume that the earth's original body is closer to the sun when it enters the gravitational plane of the sun. If it is in the position of Venus or mercury, the gravity of the sun on the earth's original body will be much greater than the inertial force of the earth's original body, and the orbit of the earth's original body will turn smaller and smaller, and finally merge into the sun
The second is to assume that the earth's original body is far away from the sun when it enters the gravitational plane of the sun. If it is in the position of Jupiter, Saturn or Uranus, the gravitational force of the sun on the earth's original body will be much smaller than that of the earth's original body, and the orbit of the earth's original body will be an ellipse, When the inertial force is too big for gravity, gravity will not hold it, the elliptical orbit will open, and the earth's origin body will run out of the solar system
The third is that only when the earth's origin body enters the gravitational plane of the sun, it is not far from the sun, so that the inertial force is equal to the attraction of the sun, the earth's origin body can revolve around the sun and become a planet in the solar system. Because the inertial force of the earth's origin body is slightly greater than the gravitational force of the sun, the earth's orbit is a circular ellipse
From the principle of the earth's revolution around the sun, we can draw the following conclusions
1、 In the same rotation system, the closer the star is to the rotation center, the faster the revolution speed is due to the greater gravity, and the slower the speed is, it will be sucked into the gravity center. The farther the star is from the rotation center, the slower the revolution speed is due to the smaller gravity, and the faster the speed is, it will run out
2、 In the solar system, large planets, asteroids and comets, no matter their size is small, speed is fast or slow, far or near from the sun, their respective inertial force must be equal to or slightly greater than the sun's gravity. The angle between gravity and inertial force is equal to 90 ° in order to revolve around the sun for a long time. If their inertial force and gravity are too different, they will disappear in the solar system
3、 Due to the different speeds of the celestial bodies before entering the solar system, the rotational speeds of the planets in the solar system are also different
4、 This theory can explain all phenomena of revolution and revolution system in the universe

Well, the rest is not. It's too long
If you ask this question, it's like asking why the sun rises in the East
The law of nature is the law of nature
Don't spray on me. I didn't read the words below. It's just my personal opinion

The title of pages 53 and 54 in the mathematics book of the fifth grade of primary school

1. Do two boxes of the same size have the same volume? Why? A: not the same, because the thickness of the board may be greater
2. The carriage of a postal freight car is a cuboid. From the inside, the length is 3M, the width is 2.5m, and the height is 2m. How many cubic meters is its volume? 3 times 2.5 times 2 = 15 cubic meters. A: 15 cubic meters
3. Fill in the appropriate volume unit on the horizontal line
A bottle of ink is about a bucket of salad oil
50 (ML) about 5 (L)
4.2.5L=(2500 ml ) 600mL=0.6L 3.25=(3250)ML 450ml=（0.45）l

Solve the equation (16-2x) × (24-4x) △ 2 = 48

4(8-x)(6-x)=48
48-14x+x²=12
x²-14x+49=13
(x-7)²=13
x=7+√13 x=7-√13

9999 and 1 / 5 + 999 and 1 / 5 + 99 and 1 / 5 + 9 and 1 / 5 + 4 and 4 / 5

9999 and 1 / 5 + 999 and 1 / 5 + 99 and 1 / 5 + 9 and 1 / 5 + 4 and 4 / 5
=10000+1000+100+10+5-1/5×5
=11115-1
=11114

How to do the second question of 116 faces in the first volume of junior high school mathematics

You write the title,

How much is the current price of an article after its original price is 100 yuan and its price has been reduced by 10% for two consecutive times

100 - (100 ／ 10) = 90 - (90 ／ 10) = 81 yuan

Let the domain of function be [1,3], then what is the domain of F (2x + 5)?

Because the definition field of function f (x) is (1,3)
So let 1 < 2x + 5 < 3
The result is - 2 ＜ x ＜ - 1
That is to say, the domain of F (2x + 5) is (- 2, - 1)

as the man tried to swinng the speedboat round.round What do you mean here?
dial the wrong number! It's swing. "Turn to" means, verb.
As the man tried to swing the speedboat round, the steering wheel cam away in his hands

Swining should be swimming
Round here is around, which can be interchanged
So what is a swimming around
The man tried to swim around the speedboat