"I talked about Taylor yesterday. Did the students understand it? Did they understand it? Did they understand it thoroughly? Did they understand it? Oh, some people understand it, some people can't figure it out."

This section is Han Daxian's mathematics class. He said: "Students who have not understood, I want to criticize you a few words. Since you don't understand, why don't you come to me? It's free to answer your academic questions. You are enrolled in cram schools outside. The tuition fee is not cheap? The most important thing in life is happiness. The most important thing in learning is fun. I can teach you mathematics, but the fun course requires you to learn by yourself. Students, are you happy?"

"hapiness!"

“Unhappy…”

Han Daxian stared at a boy: "Wang Yuhang, why are you not happy?"

The boy said awkwardly: "Teacher Han, I am Huang Yuhang..."

"Sorry, I'm wrong. Wang Yuhang is from the second class. You two look quite similar, and even your hairstyle is exactly the same. Both of them have shaved 70% and three-point hair on both sides, like brothers. So Huang Yuhang, can you tell me why you are not happy?"

Huang Yuhang dared to appeal: "Teacher Han, mathematics is the king of science. I really want to learn mathematics well, but your teaching pace is too fast. I have not yet fully understood the guidance, and you have already started talking about Taylor."

"I'm very depressed. A teacher complained that my teaching progress was conservative, but you said that my teaching pace was too fast. What are the standards? Why are you so unstable? I don't know how to attend class anymore!" Han Daxian was angry and quite aggrieved.

"Teacher Han, your teaching pace is neither fast nor slow, and the intensity is moderate. Let's hurry up and enter the teaching stage." Li Zihan spoke up righteously, and he said a fair word.

Han Daxian was in a better mood. He said with a smile: "Li Zihan's recent progress can be seen by the naked eye. I feel relieved. Li Zihan, are you happy?"

Li Zihan said happily: "I am very happy!"

Han Daxian asked again: "Why are you happy?"

Li Zihan told truthfully: "It would be very happy to learn useful knowledge in Teacher Han's mathematics class, hehehe."

Han Daxian nodded and said, "Excellent."

Next, when we entered the teaching stage, Han Daxian said: "There is still some content left to discuss the combination identity. I will first talk about the combination identity, and then talk to you about calculus."

"Combination counting and combination identity are based on the arrangement, combination and binomial theorems of high school stages. Their principles are simple, but their practical skills are extremely special. They mainly examine students' logical thinking, computing ability and flexibility."

"To be honest, combine counting, combine identity and probability to form a system. This system is self-sufficiency and self-consistent, and it is more difficult than entry-level calculus. To put it bluntly, calculus is a tool, so I put calculus to a later stage. Do you think there is any problem?"

Han Daxian has an effective teaching plan, and the city's outstanding young teachers are not a blow.

"no problem!"

"Listen attentively!"

The students were enthusiastic and listened as soon as they could understand. If they couldn’t understand, they were forced to listen. It was beneficial to open the book. It was better to listen to it than not.

(c0n)^2(c1n)^2(c2n)^2…(cnn)^2=(2n)!/n!n!·

"This formula is very representative, but if you consider using basic combination of identity to prove this problem, it is difficult, time-consuming and thankless. Don't be too irritated at this time, but need to be flexible and flexible. Students, please note that the terms on the left happen to be the square of the coefficients of the various terms in the binomial expansion formula... Li Zihan, will the parent function method be used?"

Han Daxian suddenly favored Li Zihan, and he called Li Zihan to answer the question.

As we all know, Ranger ranks first in the class in mathematics, with Li Zihan and Wu Zihan tied for second place.

Li Zihan is quite good at math. Although he has not scored in math, he often gets above 145 points.

The confident Li Zihan immediately gave an explanation: "(1x)^n(11/x)^n is equal to 1/x^n, then the term containing x^n in (1x)^2n is the n1st term in the expansion formula, and its binomial coefficient c2n is to the n power of (1x)^n(11/x)^n, so it can be proved that (2n)!/n!n!·. This is my understanding of the parent function method."

"The explanation is reasonable, the logic is clear, the thinking is flexible, and the cognition is profound." Han Daxian was not stingy in praise, saying: "Li Zihan, sit down, you have indeed made progress, you are improving every day."

Li Zihan sat down happily. He performed so well and was highly valued by Teacher Han and won the love of his classmates.

Zihan knew that the girl in the middle of the third row must be paying attention to him.

Unfortunately, Zi Han in the middle of the second row moved to the liberal arts class.

If Zihan was still in our Class 2 and 3, she would have witnessed my proud and powerful spirit with her own eyes.

Zihan was a little sad. He tried his best to prove himself in his studies, but he could not let his beloved Zihan see it.

Fortunately, Yutong is still there in Class 2 and 3.

"Using the binomial expansion as auxiliary function and comparing the coefficients of a certain term for calculation, this method is the parent function method. Li Zihan's explanation just now is basically correct, so I will give some additional explanations..."

Han Daxian spent more than ten minutes explaining in detail the application of the parent function method in combination of identities. He also said: "There is a second solution to this problem, called the mathematical model method, with n blue balls and n red balls, 2n=(2n)!/n!(2n-n)!=(2n)!/n!n!·."

"On the other hand, it can be seen as n1 ball-taking activity as: take r from n blue balls, and then (n-r) from n red balls, -rn=(crn)^2, r is equal to 0, 1, 2, 3... until n, so the number of ball-taking types that meet the question is (2n)!/n!n!·."

"This method adopts the logical thinking method of 'calculating twice', and uses the construction of a combination counting model of red and blue double-color balls to verify the answer, and transforms abstract mathematical concepts into relatively concrete practical operations."

"Whenever I encounter this type of question, I strongly recommend the mathematical model method. The mathematical model method is practical, effective and easy to use. Lottery players... Oh no, the teachers and classmates have used it and they all say it's okay. The get out of class is over."

The bell rang and Han Daxian left quickly.

KAKA.

Ranger poked Li Zihan's back neck.

Li Zihan suddenly turned around and said, "What are you doing?"

Ranjie said sincerely: "Brother Hanzi, you have become stronger again. The mother function method you gave is exactly the same as what I thought."

Li Zihan looked calm and composed: "Oh, it turns out that it is this matter, this is a trivial matter that is not worth mentioning."

Langjie continued: "Mathematical model method works, but in many cases, the parent function method and mathematical induction are more stable and have higher fault tolerance. What do you think?"

Li Zihan's body shook, and Lan Jie's words came to his heart.

"Langjie, do you have anything to do? I'll go to the bathroom if it's okay."

"Let's go together, chat while walking."

"If you are so private in the toilet, you don't have to go together!"

Li Zihan went to the bathroom alone, and Lanjie left the classroom in half a minute and came to the end of the corridor.

Lanjie was about to enter the bathroom when he suddenly saw someone walking down the stairs.

Class 11, Grade 2 (11) is upstairs, and this person is Su Zihan.

Su Zihan stopped, and she smiled and waved: "Hi, Lanjie."

After seeing Su Zihan again after many days, Lan Jie missed him very much: "Su Zihan, you have lost weight and you have lost a lot. Go to Class 11. Are you under a lot of pressure? Can you adapt to the rhythm of the liberal arts class? Are the new teachers and classmates good to you?"

Su Zihan touched her lower abdomen: "are    you    kidding   me? I just weighed last night and I gained two pounds."

"Su Zihan, your face is thin, and you look thinner. Since your weight has not dropped, I'm relieved."

"Langjie, I have been studying your physics, chemistry and biology homework for a long time. I have always wanted to invite you to dinner, but I have never encountered the right opportunity. Either I don't have time or you have something to do. It's better to meet me by chance than to invite me. I'll have a chance after school today?"

"Yes, let's get off."

"Okay, see you after school."
Chapter completed!