Hey, I want some 8th grade math and physics problems

Mathematics: 1It is known that a, b, and c are the three sides of the triangle abc, (1) when a square + 2ab = c square + 2bc, try to determine which type of triangle the triangle abc belongs to, and explain the reason.

2) Is the value of the algebraic formula a-squared-b-squared+c-squared-2ac positive or negative? Explain why.

2 Knowing a square a—2 = 3, find the value of a cubic + 2a square + 1999 (to process).

3 12345 squared — 12344 12346—1

Physics: After passing through the prism, sunlight is decomposed into various colors of light, which is a phenomenon of light. There are three colors that can be mixed properly to produce other colors, and these three colors are red light, and blue light.

18.When we are in a movie, we can see what is on the screen from all angles because of the reflection of light. At the same time, we can distinguish the voices of different characters on the screen because they are different.

19.As shown in Figure 7, there is only one small fish in the tank, while two can be observed from point a, with one fish becoming shallower and the other larger. The former is due to the formation of the image (fill in "real" or "imaginary").

When boiling water is poured into the bottle, the air in the bottle will vibrate and make a sound due to the agitation of the water flow, and the air column is longer at the beginning, the vibration frequency is small, and the sound is low-pitched; The more water is filled, the shorter the column of air, the greater the vibration frequency, and the higher the pitch of the sound produced.

Example: Cold water pours on the ground with a crisp crackling sound, while boiling water pours on the ground with a low fluttering sound. This is due to the fact that there is a lot of air in cold water, and there is almost no air in boiling water.

The volume of air is reduced, and the sound of boiling water in a boiling water bottle is produced by the vibration of the gas inside the bottle.

with the method of distillation. But fire is not recommended, because there are not enough instruments to measure temperature on the island.

The conditions that already have it: Robinson can make a fire, can use fire to make pottery (both of which are told in **), and has made sugar cane wine.

Taking advantage of these conditions, it is possible to: fire a pottery vessel that can be crooked in the shape of a gourd, the container is divided into 2 parts, a cooling part and a heating part, and the heated part is filled with sugar cane wine; The cooling part has an opening, which is plugged tightly with a plug during the heating process, and is shielded with weeds and leaves to prevent sunlight. Now expose the prepared container of sugar cane wine to the sun, and wait until it is dark when the container has completely cooled down to open the stopper and collect the relatively pure alcohol.

Of course, it can also be heated by fire, but in view of the conditions, the temperature is difficult to master, and the alcohol vapor is not easy to collect, and there will be ** and the hidden danger of fire, it is still recommended to use solar energy.

Heating the sugarcane wine at 80 degrees, the boiling point of the water is 100 degrees, the boiling point of the alcohol, and the alcohol can be volatilized and collected.

1.Because the ice becomes a convex lens, the sunlight converges under the ice surface, and the temperature of the water rises, so it does not freeze (which means that the principle of a magnifying glass is similar).

2.This is the principle of refraction of light, and when the light passes through the convex lens, it will change in a straight line, and the route will have an angle to the edge of the mirror. The magnifying glass is the convex lens used.

Does the water under the ice not freeze? It depends on how deep the water is. If the water on the road freezes, it will all freeze Harbin's physics?

Refraction of light.

1.Because the water freezes to continue to absorb heat, and this is the top has been frozen, the temperature is always 0, the water below can not continue to absorb heat, so it does not freeze

2.The magnifying glass should be a convex lens.

1.Because: the temperature has reached minus many degrees, so the water is constantly freezing, and solidification is an exothermic process, so the water under the ice does not freeze.

Ice separates water from air and cannot solidify.

2.Magnifying glasses are convex lenses, through which you can see things through convex lenses and concave lenses, and the shape of the object changes under the refraction of a certain light.

The first time the ultrasonic wave is emitted from the time it is emitted to the time when the ultrasonic wave arrives at the trolley, the trolley has moved the time, and the distance between the trolley and the ultrasonic instrument is 340m s*

The second time the ultrasonic wave is sent to the answering trolley, the trolley has been moving for 17+ The distance between the trolley and the ultrasonic instrument is 340m s*

Then, the speed at which the trolley moves is: 17

The time from the first emission of ultrasonic waves to the second reception of ultrasonic waves (17+, then the distance of the trolley during this period is (s=vt=340m s* s=5814m).

The trolley moves at a speed of v

340m/s+v）（

v=34/

During this period, the distance of the trolley is 17m, and the speed is 1ms

20km s wrong.

Known: v = 20 m s, t = 1800s

Find the length of the bridge l

Solution: l=vt=20*1800=36000m=36kmA: The length of the bridge is 36km

Physical wolf pack.

I think this car is really 20km s. Do you still need rockets (the above one is counted as 20m s, I'll count it as 20km h).

Known: The speed of the vehicle is 20km h and the time is 1800s

Seeking: How many meters is the length of the bridge.

Solution: 1800s=

Because s=vt

So s=20*

A: The length of the bridge is 10,000 meters.

Known: v=20kms t=1800s

Find :s because:v=s t

So: s=vt=20km sx1800s=3600kmA: The length of the bridge is 3600km

Solution: Set the velocity to v

v*solution gives v= m s

Answer: The speed of sound in cast iron is.

Let the total distance be 2s. Half segment is s.

s 2 + s 3 = t, t is the total motion time.

2s t is the average velocity, which is.

There is a temperature difference between the slag 357 and the slag 357, 100 equal parts, each part is, the freezing point of water is 0, higher than mercury, so under this thermometer, the freezing point of water is.

The boiling point of water is 100 higher than the freezing point, so it is 100 under this thermometer.

I don't have a calculator, you can do the math yourself.

Are you sure the numbers are correct? How could it have appeared?