What do you think is the most important way for us to understand the history of prehistoric society?

What do you think is the most important way for us to understand the history of prehistoric society?

The most important is archaeological research, followed by legends and myths

Now we know that the universe is 15 billion light-years. It takes such a long time for the speed of light to travel. How did human beings explore it?

Human "exploration" is to observe the light or radio waves emitted 15 billion years ago

How many sides does the shadow of an acute cube have in the sunlight? To be accurate, how many edges are there in the shadow? In the sun

Square - vertical illumination
Isosceles trapezoid -- oblique vertical plane
If the sun is at an angle to the surface of a cube, its projection may be a parallelogram
It can be up to six
o(∩_ ∩)o...

Among the following phenomena, the reflection of light is related to A. shadow under the sun B. seeing colorful neon at night Please. It's urgent

B is definitely B. I did it

Is the sun light AC and a'c 'parallel, the same height at the same time, the shadow of the wooden pole under the sunlight is the same length? It is not stated in the title that two wooden poles are perpendicular to the ground. We should realize that two wooden poles of different lengths can be of equal height in the same plane. For example, in a right angle triangle, the height of all corners and bevels is the same, but the lengths of right angles and oblique sides are absolutely different, We can draw a conclusion that the shadow is not the same long

We know that the earth is round, and at the same time, the places are different

As shown in the figure, the sun light AC and a'c'are parallel. At the same time, the shadow of two poles with the same height under the sunlight is the same length? Tell me your reasons

The shadow is as long
prove:
∵AB⊥BC，A′B′⊥B′C′
∴∠ABC=∠A′B′C′=90°
∵AC∥A′C′
∴∠ACB=∠A′C′B′
In △ ABC and △ a ′ B ′ C ′,
∠ABC＝∠A′B′C′
∠ACB＝∠A′C′B′
AB＝A′B′
∴△ABC≌△A′B′C′（AAS）
∴BC=B′C′
It's as long as the shadow

The sun light is parallel light. Is the shadow of two cement poles with the same height under the sunlight irradiation the same length? Explain why

Different, the same height of the cement pole with different angles with the sun, the shadow is not the same, for example, one vertical 90 degrees, one tilt 45 degrees

AC and a'c 'are parallel in the sunlight. Do two poles with the same height at the same time have the same shadow under the sunlight? Tell me your reason To process (the review of the triangle in the fifth chapter of the second semester of junior high school) It's better to have proof

It's the same, because at the same time, the sun is at the same angle as the two poles

As shown in the figure, the sun light AC and a'c'are parallel. At the same time, the shadow of two buildings under the sun is the same length. Is the building the same height? Explain why

The building is the same height
It is proved that: ∵ ab ⊥ BC, a ′ B ⊥ B ′ C ′,
∴∠ABC=∠A′B′C′=90°，
∵AC∥A′C′，
∴∠ACB=∠A′C′B′，
In △ ABC and △ a ′ B ′ C ′,
∠ABC＝∠A′B′C′
BC＝B′C′
∠ACB＝∠A′C′B′ ，
∴△ABC≌△A′B′C′（ASA）
∴AB=A′B′．
It is the same height as a building

The projection of two objects of different length under the same sunlight at the same time and place is () A. Equality B. Longer C. Short and long D. Not sure

Because we don't know the position of the two objects, we can't compare them