Since Zhang Han dared to take out the "Notes on the Nine Chapters", he was also sure. In the "Annotations to the Nine Chapters", Zhang Han used punctuation for the first time and wrote a preface to explain the significance of punctuation. and how to use it, this is one of them. Zhang Han also gave proof of some definite theorems in Chapter 9, for example, he proved the Pythagorean theorem using the square inner trigonometry, which is the second. Zhang Han also gave the detailed steps of solving the problem in "Nine Chapters of Arithmetic", and put forward many new ideas, such as using multiple systems of equations to solve the problem of insufficient surplus. This is the third. Moreover, Zhang Han also used the secant circle method to find the volume of the sphere, and the area of the sphere by the integral method, and calculated the pi rate of 3.1416 by the area of the circle approximated by the inscribed regular polygon.

Guan Ning looked at it slightly, and he couldn't let go of his eyes, and his fingers pinched and estimated, and he counted it. Mathematics is not something that can be read in a while, and every problem needs to be calculated and studied repeatedly to understand. Several people present were of different levels, and they were divided into three groups around the three books, leaving Zhang Han aside. Wang Lie looked at it for a while, didn't see any mistakes, and nodded at Zhang Han to show his praise while others were unprepared.

Zhang Han was ashamed of it, and bowed slightly with a smile on his face, expressing his gratitude. Mathematics is the foundation of all disciplines, Zhang Han has no intention of secrecy, and has recorded the proof process in detail in the book, so that people can understand it at a glance.

"Brother Zhang, little brother Yulu, may I ask what ......is the volume of this ball?"

"Ah, Brother Guan is polite. This circumcision method, as the name suggests, is to cut the ball into countless pieces, and each sphere can basically be calculated as a cylinder...... Oh, it's not that I don't understand ...... here."

Zhang Han talked to Guan Ning for a long time, and had to take a pen and draw a sketch before explaining the matter. Zhang Han applied the Pythagorean theorem to prove that the volume of a sphere is two-thirds of the volume of a cylinder of equal diameter and height by proving that the volume of the sphere is equal to the volume of the removed part of the cylinder of equal diameter and height. Guan Ning flipped to this circumcision method, but ignored the figure drawn on the other side. Calculus is inherently abstract, and without graphics, it would be even more difficult to understand.

After talking about the volume of the sphere, Zhang Han began to prove the Pythagorean theorem again, and several people also raised several difficult questions, and Zhang Han answered them one by one.

Speaking of this, Zhang Han is a strong point, and he has been teaching in ethnology for several years, and he is familiar with these things.

"May I ask Brother Zhang, I don't know what Brother Zhang is?"

"Ah, this, it's a character that Zhang Han made up randomly, and it's easier to use it for calculations......"

The troubles of people are good teachers. Zhang Han is also expressive, and when it comes to the rise, Arabic numerals are used. was asked by Hua Xin, so he had to say that he made it up by himself and explained it briefly.

Just as Zhang Han was foaming at the mouth in the hall, in an embroidery room in the backyard, there was a young girl pacing from east to west and from west to east in the house. The girl was only thirteen or fourteen years old, with a beautiful appearance and a gentle temperament, with goose-yellow cedar and a striped skirt, tied with a silk belt around her waist, and a black and towering cloud sideburns on her head, a goose-egg face was very delicate, her eyebrows were like a crescent moon, and her eyes were full of autumn water.

Since the gift brought by Zhang Han yesterday, Wang Yan panicked in his heart, and sent Xiaoya, who was close to him, to the front in the morning to inquire about the news. But before she came back, she couldn't sit still, and she couldn't calm down. There are many people who marry at the age of fourteen or fifteen in the Great Han Kingdom, and Wang Yan is not ignorant of this.

Wang Yan knew Zhang Han for a long time, when she was still an ignorant child, and she was very happy to see those exquisite gifts. Thinking about this, she couldn't help but be a little funny, she was really ashamed. In the past two years, she has heard a lot about Zhang Han, and has corresponded with Zhang Han from time to time, but she has never known what kind of person Zhang Han is.

It is said that the Zhang family of Suxian County had a close relationship with Zhang Rang, the leader of the Ten Standing Attendants; It is said that the rich family of the Zhang family in Wuxian County; It is said that he was a child prodigy, and at the age of one he spoke very well; It is said that he was very filial and told stories to his mother at a young age; It is said that he is a good storyteller and can tell hundreds of stories; It is said that his handwriting is also very good......

The wealth of the Zhang family can be seen from the gifts sent by the Zhang family from time to time. Although the Zhang family never gave valuables, the gifts they sent were all exquisite. During the New Year's holidays, what was given to his father Wang Lie was just some pen and paper, books and wine, and most of the things given to his mother were ordinary things, and only the things given to her were a little more luxurious.

She also knew that he had a horse called Big Black, but he was smart; There was a lazy dog named Little Black, who was fat and didn't look good; There is a treasure knife, blowing hair and breaking hair; He rode the big black to hunt in the summer, smashed the glacier to fish in the winter, and went to release the paper harrier in the spring and autumn......

Wang Yan is very familiar with him, but also very unfamiliar, what kind of person will he be? What does it look like?

After turning around the ground countless times, Wang Yan saw several boxes on the side, which were gifts from Zhang Han, some were sent yesterday and some were sent before.

There was a soft (cotton) cloth, soft, warm, dyed bright and dazzling purple, so bright, her favorite color; There is a palm-sized glass mirror, inlaid in a small and delicate silver box, much brighter than the bronze mirror; There was a whole set of "Tales Collected by him", which he copied to her one after another; There is a box, which can be opened layer by layer, divided into twelve grids, containing twelve kinds of dried fruits and preserved fruits such as ginkgo seeds, walnuts, and dried pu pottery; There was also an same box, but it was full of sweets, including hemp sugar, toffee, halva...... There are also twelve.

Wang Yan was still a child, and unconsciously, she had forgotten Zhang Han and took out a piece of hemp candy from the box. She prefers hemp candy to toffee, and the more she chews, the more fragrant it becomes.

"Miss, Miss~"

"What's the matter? Panicked. ”

“……”

Xiaoya is still a yellow-haired girl, two years younger than Wang Yan, she wears a lilac cedar skirt, a small melon seed face, delicate and lovely, running all the way back from the outer courtyard, panting, and not speaking for a long time.

"The man, the man is coming."

"Who, ah......"

Wang Yan's face turned red, her mind was all on the sugar, and she didn't remember who Xiaoya was talking about for a while, but she immediately remembered.

"That's the man~"

Xiao Ya let out a long voice, making Wang Yan's face red like an apple.

"Who knows who you're talking about......"

"Hey, hey, hey......"

Xiao Ya stared at Wang Yan with a wicked smile and didn't speak. Soon, Wang Yan couldn't stand it anymore, even his neck was red, and he couldn't help but be annoyed and angry, put the candy down, grabbed Xiaoya and began to tickle her.

"No, no, spare me, miss, good miss......"

Xiaoya was very sensitive, and in the scratching of Wang Yan's eyes, she soon couldn't stand it anymore and gasped and surrendered.

Xiao Yabai ate a lot of hemp candy from her, and after talking for a long time, she didn't tell what Zhang Han looked like, and Wang Yan didn't see Zhang Han himself until dinner.

He is not very good-looking, a round face, thick eyebrows and big eyes, quite a bit heroic, a pair of warm eyes, black and white, faintly containing a smile, but turning the heroic spirit into invisible, before he spoke, he opened his mouth to laugh, and laughed innocently, but Wang Yan always felt that there was a hint of cunning in that smile. In the spotlight of everyone, Wang's pink face was slightly red, and he generously gave Zhang Han a salute, and Zhang Han also returned the salute in a proper manner. The little girl was gentle and gentle, and the curiosity and shyness in her eyes were clear, but Zhang Han could see it clearly.

This was the first time Zhang Han and Wang Yan met, and both parties left a good impression.

[Be kind, read a book and smash the ticket]

PS: There are two more.