Euler's formula: Suppose the number of vertices of a convex polyhedron is v, the number of edges is e, and the number of faces is f, then vf-e=2.

When he was learning polyhedron and learning an Euler formula again, Liu Yichen was speechless. He didn't know which Euler formula he had encountered and wanted to learn.

Euler formula, not only one, but many. It refers to many formulas named after Euler. In the history of mathematics, many formulas were discovered by Euler. They are all called Euler formulas. Euler formulas are scattered in various mathematical branches.

Euler, whose full name is Leonhard Euler, is a Swiss mathematician and physics community. He is one of the pioneers of modern mathematics. This is a master of mathematics who has to learn when learning mathematics, because when you learn mathematics, you will find various Euler formulas. Euler formulas are a hurdle that you cannot avoid when you study mathematics.

Of course, he is also very legendary. He entered the University of Basel at the age of 13, graduated from university at the age of 15, and obtained a master's degree at the age of 16. In other words, when he was 16, everyone had just been in high school, and Ola had already graduated from a master's degree. This is definitely a matter of being more popular than others, and it is necessary to throw away the goods.

Of course, the more you understand him, the more you will be respectful to him. According to the information found by Liu Yichen, Euler is an extremely prolific mathematician. It is not easy for others to make a paper a year. However, Euler has to write more than 800 pages of paper every year on average, and has also written a large number of textbooks such as mechanics, analysis, and geometry. "Introduction to Infinite Small Analysis", "Principles of Differential Studies", "Principles of Integral Studies", etc. have all become classic works in mathematics.

It is also his unparalleled proficiency that makes it possible to see important constants, formulas and theorems named after him often in many branches of mathematics.

The most terrifying thing is that in the last seven years of his life, Euler was completely blind, but despite this, Euler still produced half of his works at an astonishing speed.

In addition to his outstanding achievements in mathematics, Euler also achieved outstanding achievements in physics. He is the founder of rigid body mechanics and fluid mechanics and the pioneer of the theory of stability of elastic systems.

"This Euler is worthy of being ranked among the 'Four Great Masters' in the history of mathematics with Archimedes, Newton and Gauss!" Liu Yichen sighed secretly.

Including when Yang Zhendong was talking about the history of the development of mathematics, Euler appeared very frequently, and Yang Zhendong gave Euler a very high evaluation, even like Euler's believer.

After reading Euler's formula, Liu Yichen got up and moved, rubbed his eyes, and studied and wrote for a long time, which made his eyes sour and tired.

When I opened the room door, I saw Liu Tingting wearing pajamas and wearing a quilt watching TV. Liu Yichen suddenly felt that he was a little envious of Liu Tingting. This life seemed to be quite good.

"Liu Yichen, school will start tomorrow. Can you watch TV if you don't watch it?" Liu Tingting asked.

"What's the best thing about TV? It's just the beginning of school. I've been studying well in school. I've been a little degenerate during this period." Liu Yichen twisted his waist and moved for a while.

"Change... state!" Liu Tingting couldn't help but say. She couldn't imagine that Liu Yichen helped her make up for her lessons every day, checked her homework, and studied until twelve o'clock in the evening. She just lived like a purgatory, and even said that she was degenerate: "You are still not a human being. Apart from studying, you don't have a life? It's too boring. You can't find a girlfriend like this!"

"Study is life, girlfriend? Why do you want a girlfriend?" Liu Yichen said disdainfully: "It's because I don't want to find a girlfriend. If I want to find one, I can guarantee that countless beauties will come over and throw themselves into their arms."

"If you don't work hard at a young age, you will be sad~~~ If you don't study hard now, you won't have time to regret it in the future!" Liu Yichen curled his lips and said, "After the start of school, remember to follow the method I teach you, first prepare for the compulsory math 4, and the same is true for other electives. Don't fail the midterm exam at that time, Lao Liu will give you another meal of bamboo stewed lean meat!"

"I will fail the exam? I will underestimate me too much!" Liu Tingting couldn't help but stand up from the quilt, looking very angry: "I am invincible, will I fail the exam?!"

Liu Yichen rolled his eyes. This girl has watched too many youth idol dramas and is terminally ill!

"It's getting late, so I'll register tomorrow. If you go to bed too late, don't be able to get up." Liu Yichen said.

To be honest, he couldn't wait to start school. It was a waste of his time at home. If it weren't for the winter vacation, the library would not be opened and the dormitory building would be closed. Liu Yichen wanted to go directly to stay in the dormitory and be peaceful and comfortable alone.

"I don't know. Our No. 2 Middle School will register tomorrow afternoon. It's nothing to do. I'll just get a book and clean the dormitory!" Liu Tingting said.

Oh, I've become an old fry.

Liu Yichen looked at Liu Tingting in surprise, but he didn't expect that this girl would become an old man and could see through it thoroughly.

In fact, the registration for No. 1 Middle School is also tomorrow afternoon. Because if you register in the morning, students from other townships will not have time to take the bus. Registration is indeed to fill in the relevant information, know where your new dormitory is, which class you are assigned to, your new student ID and student number, as well as to receive books, homework books and stationery for the new semester, etc.

Even on the first day of school, there will be only a start-up ceremony, followed by a campus cleaning, classrooms, etc.

After a little rest, Liu Yichen continued to read the book and began to learn number theory. Number theory is one of the most important fields of mathematics, and is a theory that specializes in studying the properties of integers. The basic element of integers is prime numbers, so the essence of number theory is the study of the properties of prime numbers. The high school number theory is elementary number theory, that is, classical number theory, which uses the properties of integers themselves (opposite, even, integer, concurrence) and logical reasoning to argue number theory propositions.

This is also one of the important sectors of Olympiad mathematics. The proportion is no less than geometry. It is different from the previous geometry, which is mostly geometric figures. Number theory has become various mathematical symbols and formulas.

In preliminary number theory, the basic principles of the two counts are the principle of multiplication and the principle of addition. It seems simple, but it is not simple.

How to say that geometry requires a strong abstract imagination and drawing ability, then number theory needs to be more sensitive to numbers, and the same requires understanding and understanding.

In this case, rote memorization is useless, because this number theory focuses on logic and thinking. It changes rapidly. Once it changes slightly, or the definition domain changes slightly, the result will change.

A proof question sometimes asks you to verify whether it is true, which means it may be true or not. It is useless for you to memorize it by rote, because the test questions will never be exactly the same.

Seeing that he had a headache, Liu Yichen rubbed his temples and looked at the clock on the wall. It was already twelve o'clock and was a little dizzy. Liu Yichen put the book, draft paper and pen into his backpack. As for the clothes and quilts, Mr. Deng had already packed all of them for him during the day.

Lying on the bed, Liu Yichen did not fall asleep directly. His mind was about elementary number theory. In fact, he studied elementary number theory in high school mathematics elective 4-6, including prime numbers and their discriminant formulas, as well as congruent and congruent equations, but there was no Ailatus filtering method to determine whether a prime is a prime number, nor would he talk about the Ferma conjecture, Mason conjecture, twin prime number conjecture, nor would he introduce the four square theorem.

"It is difficult to change the elective 4-6, which is called the preliminary basic number theory. The cover title is really perfect!" Liu Yichen laughed secretly.

In the past, he thought that the primary number theory was just like that, but now he is further studying the primary number theory, but he found that what he had mastered before was the preliminary basic number theory, and when it comes to playing word games, Chinese people are indeed the best at it.

Then Liu Yichen was immersed in the system sub-interface and saw that after a winter vacation efforts, his various aspects had been greatly improved:

a:Mathematics:lv5(30/200)

b:Physics:lv5(2/200)

c:Biology:lv4(10/120)

d:Chemistry:lv4(80/120)

e: Chinese: lv2(20/50)

f:English:lv2(20/50)

Points: 300

Lifespan of the upper left corner: 366 days

It can be said that during the winter vacation, his abilities were improved in all aspects, especially in the four subjects of mathematics, physics, chemistry, and biology. As for Chinese, English, and some improvements in English did not stop.

Mathematics reaches lv5, which means that Liu Yichen is already a math master in mathematics, and is definitely ahead of most senior high school students.

Thanks to the improvement of mathematical ability, Liu Yichen learned physics competition knowledge much faster and accelerated his understanding, which made physics reach lv5 level.

If it weren't for spending part of his time on Liu Tingting, Liu Yichen could at least improve chemistry to the lv5 level.

However, overall, Liu Yichen is still very satisfied with the effect of the winter vacation, whether it is the "Save Sister Plan" or the plan to become stronger by herself. After all, the winter vacation is only one month long, and it is not like the summer vacation to have more than two months.

"Start tomorrow, continue to start high school life!" Liu Yichen said to himself.

In a daze, Liu Yichen seemed to have a dream. He dreamed that he won the first prize in the Mathematical Olympiad competition area, went to participate in the winter camp, won the gold medal in the winter camp, and created the historical record of Qingcheng No. 1 Middle School. When he returned to Qingcheng No. 1 Middle School, he was very concerned about the attention of the media and took photos, and he left his name in history.

He dreamed that he saw a foreigner, and he said his name was Euler, and then said a bunch of things he couldn't understand. Liu Yichen couldn't understand no matter how much he listened, and he didn't know what language Euler was speaking.

In a daze, he had many dreams, dreaming that he was answering questions nervously in the examination room, and then seemed to forget to bring 2b pencils. The invigilator surrounded him and scolded him. He started arguing with the invigilator, was kicked out of the examination room, recorded in the examination file, and was unable to take the examination from then on.

He was dissatisfied and appealed, but no matter how he appealed, he was rejected and he was unwilling to pay attention to him.
Chapter completed!