Mathematical diary about decimal division (about 200 words), mathematical diary about polygon area (about 260 words)

Mathematical diary about decimal division (about 200 words), mathematical diary about polygon area (about 260 words)

Decimal division
If the middle point of "123" is an insignificant decimal point, it becomes "1.23" or "12.3". If "456" is also an insignificant decimal point, it becomes "4.56" or "45.6" Decimal point is such a magic symbol, it can make all numbers become "small"!
In unit 7, we learned the multiplication and division of decimals, which made me feel a lot!
The first point: the number of digits should be aligned when the column is vertical. When the column is vertical, many students often mistakenly think that it is to align integers with integers, and decimal with decimals. If they do that, it's a big mistake! The correct way should be like this: no matter where the decimal point is, the end of two numbers must be aligned when the column is vertical, The results and answers can be correct!
The second point: in the process of vertical column, you must not point the decimal point. This point is a common fault of many students. If you point the decimal point in the exam, you will be deducted. How sorry you are!
Third point: be careful. Multiply a decimal by 101001000 Or a decimal divided by 101001000 Must not move the decimal point in the wrong position and direction!
Let's study mathematics seriously and devote ourselves to it. There are many secrets in the kingdom of decimals waiting for us to explore!
Polygon area
The mathematical "genius" bee hive in animals is a strict hexagonal cylinder, with a flat hexagonal opening at one end and a closed hexagonal rhomboid bottom at the other end. It is composed of three identical rhombus. The obtuse angle of the rhombus forming the chassis is 109 degrees 28 minutes, and all the acute angles are 70 degrees 32 minutes, which is both firm and material-saving. The wall of the hive is 0.073 mm thick, The error is very small. Red crowned cranes always migrate in groups, The angle of the figure is 110 degrees. More accurate calculation also shows that half of the angle between the figure and the direction of the cranes is 54 degrees, 44 minutes and 8 seconds! And the angle of the diamond crystal is 54 degrees, 44 minutes and 8 seconds! Is it a coincidence or some kind of tacit understanding of nature? The spider's "eight trigrams" web, It's a complex and beautiful octagonal geometric pattern. It's difficult for people to draw a symmetrical pattern like spider web even with the compass of a ruler. In winter, cats always hold their bodies into a sphere when they sleep. There is also mathematics in this process, because the sphere makes the surface area of the body the smallest, The real "genius" of mathematics is the coral. The coral keeps a "calendar" on its own body, and they "paint" 365 stripes on its body wall every year, apparently one every day. Curiously, paleontologists found that coral 350 million years ago "painted" 400 "watercolours" every year. Astronomers told us that, At that time, the earth only 21.9 hours a day, a year is not 365 days, but 400 days

About 300 ~ 400 words
How to write a math diary? You'd better send 2 or 3 articles

On Tuesday, June 28th, at noon today, I was doing my summer math homework. Unfortunately, I met a very difficult problem. I thought about it for a long time, but I didn't come up with a solution. However, this problem is like this: there is a cuboid, the product of the front and the top two areas is 209 square centimeters, and the length, width and height are prime numbers

Be in a hurry

Mysterious leap year
Today, in reviewing the time unit, the teacher mentioned the normal year leap year. The leap year is a year that only occurs once every four years. In that year, there will be 29 days in February and 366 days in the whole year. I can understand this, because the time of the earth's revolution is 365 days, about 1 / 4 days. After four years, there will be one more day, which will be added to February with the least number of days
However, what I can't understand most is why a year with an integer of 100 is a leap year if it is a multiple of 400. For example, 1900 and 1800 can be divided by 4, so it should also be a leap year. Why must it be a multiple of 400?
In order to find the answer, I looked through the books, but I didn't find the answer, only got a data, the time of the earth's revolution is 365 days, 5:48:46 seconds, I thought: eh, maybe it can be calculated through this
I first convert 5:46 seconds into 20926 seconds, and a day has 86400 seconds. This is the number of days that people seldom calculate every year. Therefore, multiplying this number by 4 equals 0.9688 days. For convenience, people regard it as a day. In this way, they calculate 1-0.9688 = 0.032 (days) = 46 minutes 4.8 seconds, and then 46 minutes 4.8 seconds × (100 △ 4) = 19:12, That is, the extra time calculated in every 100 years is regarded as one day, which is not pasted on other 99 (100-1) years. In this way, the extra 24-19.2 = 4.8 hours is calculated. In this way, the extra 4.8 × (400 △ 100) = 19.2 days is calculated in every 400 years, which is close to one day. Therefore, there is another leap year in 400 years, that is, 100-3 = 97, so there are only 97 leap years in every 400 years
Oh! It turns out that my kung fu is not inferior to those who want to do it. I finally worked it out. Although it's troublesome, it also unties one of my heart knots. That's great. In fact, mathematics is very close to our life, almost everywhere. As long as we are careful, there will be a lot of harvest!
three hundred and thirty-six