The happy New Year is over, and Geng Xiaofan remembers about learning too much.

I promised the Queen Mother, but it has been more than half a year, and I haven't gone to class once. Listening to Yang A's meaning, Wang Xian was dealing with it for him, and he couldn't help but be grateful.

Prepared a generous gift and personally came to the door to thank you. Moreover, he hadn't seen Jing Yan for a year, so he had to take this opportunity to be relieved.

When he came to Wang Xian's living room, he found that Wang Qu was also there.

"Sir, long time no see, is this always good?" Wang Qu took the initiative to give a salute to Geng Xiaofan.

"Good, good! I've been busy with housework since I came back, I don't know if Brother Jujun is okay? Geng Xiaofan hurried back.

"Maoling Chang'an said that it is not far away, it is not close to it, Jujun has been busy with Taixue this year, it is rare to have time, there have been two visits to the door, but when I inquired, Mr. is not at home, and he has not been able to make the trip. I hope you forgive me! ”

"I should have gone to visit my wife, I did pass by Chang'an a few times, and I was always delayed by some chores.

"Yes, Mr. Lou often goes, often sends some soups and medicines, and the two of them often learn from each other."

"Oh! That's good! I wonder what Brother Jujun is busy with today? ”

"He's in the back garden, and he's asking Miss Wang for something, hehe!" Wang Qushi smiled happily.

"Ahh He's coming, too! I'll see you later. Geng Xiaofan was a little surprised, how did this Wang Mang get together with Sister Jing Yan?

"The prince is now studying arithmetic, and I don't know who told him that the little girl is proficient in this way, so he came here. My daughter is also strange, I have never seen her learn, how can she be proficient? Wang Xian also couldn't figure it out.

"Indeed, Sister Jing Yan's arithmetic is indeed perfect, it is estimated that she has been trained by the princess, the so-called arithmetic is actually simple, as long as you open your mind, you can understand everything."

Geng Xiaofan was sloppy, Jing Yan's sister is a college undergraduate, and she still studies financial management, she is not an ordinary person!

"Lan'er, go see Miss and Jujun, and invite them over." Wang Xian sent someone to invite him.

"Don't worry, I'll go see them later, don't disturb them. I'm here today mainly to thank Dr. Wang. ”

"Thank me?" Wang Xian was a little strange.

"I promised the Queen Mother to go to Taixue to give a lecture for one day every month, which has been more than half a year, and I haven't gone once, thanks to Dr. Wang's transfer!"

"Hehe, this! You really have to thank me, every time I speak for you under your banner. Hehe! ”

"Shame on you!" Geng Xiaofan hurriedly saluted Wang Xianshen.

"The lord is here today, is he ready to go to Taixue to teach?" Wang Xian also guessed Geng Xiaofan's intention.

"Hey! I'm also talkative, and I brawn a few words in front of the Queen Mother, but I didn't expect to be right to her old man's stomach, and I was also forced to do so! ”

"Hehe, Lord Geng is too modest, since you are ready, then go once a month on the fifth day of the new year!"

"Yes! However, I have never talked about it, can you let me follow you once or twice first, and I will have a bottom in my heart? ”

"No problem, on the twentieth day of the first month, Taixue will start classes, and the lord can go with me."

"Yes!" Geng Xiaofan put his mind at ease and listened to him for a "lesson" or two, and he still had time to prepare.

After chatting with Wang Xian for a while, Geng Xiaofan said goodbye, he really wanted to see how Sister Jing Yan taught Wang Mang.

As soon as he arrived at the door of the back hall, Geng Xiaofan heard Wang Mang's voice, "Miss Wang, this ninety-nine calculation is really easy to use, I don't know if there is any division?" "Dogs

"Huh!" Geng Xiaofan smiled, this Wang Mang is really stupid, with a multiplication formula, what more division formula! Division is nothing but the inverse of multiplication.

Wang Jingyan was also made out of temper by Wang Mang's "unenlightened", and she was a little happy to see Geng Xiaofan outside the door.

"Brother Xiaofan, I'm too stupid, it's better for you to teach the giant monarch!"

"Hehe, is this going to learn division?" Geng Xiaofan was not polite and went straight to the door.

"That's not it, the prince of Jujun is studying the "Zhou Ji Sutra", you can tell him!" Wang Jingyan was relieved.

""Zhou Ji Sutra", I remember ......" Geng Xiaofan remembered that the Zhou Ji Sutra was the first to record the Pythagorean theorem, as if it was to explain this, what is so difficult about this.

"To put it simply, it is the hook three strands, four strings and five ......" Geng Xiaofan picked up the pen and drew a right triangle on the wooden board, and began to explain the "Pythagorean theorem" to Wang Mang.

"I understand this, so if this Pythagorean is not a moment, can't it be counted like this?" Although Wang Mang understood, he raised questions again.

"It can be calculated, but it is a little troublesome, and it is necessary to calculate the diagonal cosine. The square of any side of the triangle is equal to the sum of the squares of the other two sides minus twice the product of the cosine of the angle between the two sides and them......" Geng Xiaofan said as if he were in a hurry, but Wang Mang was confused.

"What angle? What squared? And what is cosine? ”

"The angle is the angle composed of two sides, the square is, it is to multiply yourself, and the cosine is ......" Geng Xiaofan couldn't go on, Wang Jingyan laughed softly on the side.

"Hey! This is really not something that can be explained in a while. However, how did Brother Jujun think of learning this? Geng Xiaofan sighed.

"Taixue's classmate is good at astronomy, and he recommended me to read this book." Wang Mang explained.

"Falling? Who is he? When Wang Jingyan heard the name Luo Xiajun, she suddenly became interested.

"Do you know that the fallen prince?" Wang Mang was a little surprised, "Luo Xia Jun is the great-grandson of Luo Xia Gong." ”

"Jing Yan, who is Luo Hong?" Geng Xiaofan was also a little curious.

"Luo Xia Hong is a famous astronomer in the Western Han Dynasty. Brother Xiaofan, do you know "The Primal Calendar"? He made it up. Wang Jingyan explained.

"Oh!" Geng Xiaofan didn't have much research on astronomy, but he seemed to have heard of the Taichu calendar, and he didn't care too much.

"Western Han?" Wang Mang looked at Wang Jingyan suspiciously.

Wang Jingyan found that she had missed her mouth, and she had an idea, "Rare, that is, rare, almost unique." ”

"Oh, that's it!" Wang Mang will be skeptical.

"Jujun Gongzi, there is a specialization in the art industry, astronomy is a university question, if you are interested in this, you must spend your whole life to participate in research, otherwise, you only need to know a little bit about it." Geng Xiaofan persuaded.

"Indeed, it doesn't seem to be of much use." Wang Mang scratched his head.

"Of course it works, and this Pythagorean theorem is very useful, especially in the military!" Geng Xiaofan couldn't help but talk more.

"Military? What's the use? Wang Mang was puzzled.

"It was so useful! For example, if you want to siege a city, how far away can you shoot a bow and arrow? As long as we know the height of the city and the range of the bow and arrow, we can roughly calculate it. Geng Xiaofan pointed to the triangle he had drawn and explained to Wang Mang.

"But how do we know that this city is high?"

"Proportional algorithm, you can use the shadow of the tower."

Seeing that Wang Mang was puzzled, Geng Xiaofan added a parallel line to the big triangle he had just drawn to form two proportional triangles.