"Be magnanimous. If you're late, you'll be late. Can't you just walk in the front door?"

Gan!

I'm not afraid to disturb your class.

Isn't it international practice for late comers to enter through the back door?

A pair of eyes to see over, even if the skin is still relatively thick, Hao Yun also a little embarrassed.

Just as he was hesitating whether to walk through the front door again, Li Xuesong on the stage coughed and continued with a straight face.

"What about homework?"

Do, homework?

On hearing this, Hao Yun was embarrassed.

"Well, I forgot."

Forgot to bring it?

ha-ha!

If you don't write it, you don't write it. You still make such low-level excuses.

Looking at Hao Yun with a smile, Li Xuesong continued: "forget to bring it? OK. You mean it's written? Anyway, there's only one question. Is it OK for you to write it now? "

With that, he tapped on the blackboard with his index finger.

"Come here and write."

Hearing the old professor's words, there was a commotion in the class, and many people began to whisper.

Hao Yun, who was standing in the back row, could not hear clearly what they were talking about. He just wanted to make complaints about the old professor. I didn't do anything hurtful, but I was a minute or two late. As for being so difficult.

Looking at Lao Li's smiling face, he knew that he was doomed today.

In his heart, he cursed the second product who had complied with his draft. Hao Yun sighed and finally walked towards the platform.

As he passed the front row, he noticed that Zheng Xueqian was shaking his eyes wildly to deliver a message and poking the screen of his mobile phone, as if to signal him to read wechat.

Are you crazy?! Actually come up? No one can write that question!]

Although I can guess that this good brother probably sent the answers to his homework to himself, he has already come here, and obviously he has no chance to take out his mobile phone.

Hao Yun gave him a reassuring look and made eye contact.

Don't worry, I'm fine

On the "self-confident" eyes, Zheng Xueqian was blinded for a moment.

what the fuck?

What does this guy mean?

Can't... Really write it out?

It's impossible!

The problem that he Shen didn't write

The touch of his eyes was just a moment. Before he could confirm whether he was wrong, Zheng Xueqian watched Hao Yun stand on the platform.

After taking the chalk from Lao Li's hand, Hao Yun stood in front of the blackboard for a while and suddenly turned back with embarrassment.

"Well, what's the title... I didn't memorize it."

On hearing this sentence, Li Xuesong laughed and said, "I'll see when you're going to perform. I pointed to the platform with my chin.".

"There are so many on the table, you can copy one at will."

A copy is OK

Aren't you afraid I'll see the answer?

Hao Yun, who picked up the top assignment, muttered a few words in his heart. However, just after opening it, he was stunned.

Good guy, I wrote a "solution".

Is this not going to be divided as usual?

At least hide the book down!

Another look at the name, it's actually Liang Ziyuan's.

Silently wrote down the title, Hao Yun was very generous to help him put the homework to the bottom.

Taking a panoramic view of the student's small movements, Li Xuesong laughed and did not tear them down. He just picked his eyebrows and continued.

"Now you know the title?"

"Well, I remember."

"Remember? OK, then stop talking nonsense and start writing quickly

Originally, it was not a particularly difficult topic. Even there were only a few letters. All the information in the stem of the topic could be explained in two sentences.

Hao Yun didn't think much about it, so he turned around and copied the title on the blackboard, and then read it carefully from beginning to end again.

However, this copy doesn't matter.

When he copied the title and read it again, the whole person was stunned.

Let positive integers a and B satisfy (a) ²+ b ²）/（ AB + 1) = k ∈ n, proving that K is the square of a positive integer

good heavens.

This question

A little familiar?

Seeing Hao Yun's inaction for a long time, Li Xuesong thought he couldn't, so he joked with a smile: "if you can write it out, you won't have to go to my class in the future. I'll give you all the credits."

Hao Yun swallowed his saliva and couldn't believe it.

"... really?"

"Oh, I need to lie to you?"

Then I really wrote

After confirming that this guy didn't seem to be saying ironic things, Hao Yun hesitated for a moment. Finally, he pasted the chalk on the blackboard and started to write.

Let K not be the square of a positive integer, then a ≠ B

Consider the Diophantine equation a ²－ kab+（b ²－ k) If a = B, then k = 1 can be deduced, which contradicts the hypothesis

Let a 〉 B 〉 0 and take a set of solutions (A0, B0) to minimize A0 + B0

Although he copied this question in the draft book before, Hao Yun never took the time to read it carefully, otherwise he would not be surprised.

And the reason for surprise is simple.

Because this is not only an original question, but also the sixth question of the 1988 IMO International Mathematics Competition on the earth!

As for why he knew

It's not because he participated in that competition, but because just yesterday, he saw it in the advanced mathematics textbook full of notes, and finally did it himself.

He even remembered that the problem was copied in the blank space at the end of the page of Veda's theorem.

According to Professor Lu's remarks, none of the examiners made this seemingly simple number theory question. Finally, they asked four number theory experts from Australia, the host of the contest, for help, but they were at a loss for a long time.

Because the experts can't work out this problem within the prescribed time, this problem has become a legend.

A total of hundreds of contestants, only a dozen of them wrote their answers in the end, and one of them even won a special prize from the main examination committee for his beautiful answers.

At the moment, he is writing on the blackboard, which is the "standard answer" that was awarded the special prize that year.

It is very interesting that according to Professor Lu's writing, these ten contestants who wrote the answers all became famous figures in the field of mathematics. When commenting on this little-known past, the professor wrote with emotion——

Generally, mathematics is the product of intuition, but some counter intuitive propositions are not excluded. Just as our common sense always tells us that counter evidence is unreliable, our common sense occasionally deceives ourselves against it

It's just a bit of a surprise to me. Even Tao zhequan, who should not have lost to this question, unfortunately fell on it

Although he has no special interest in mathematics, and Hao Yun has never heard of the names mentioned by the professor, he still draws a reliable conclusion from the limited annotation.

This note is probably the relic of a famous person - or even a great man in his previous life?

When I think about it, I suddenly feel like a relic.

The only pity is that when he finished reading the note, the system didn't even give him any ash left, and directly erased the existence of that thing from the world.

While Hao Yun was thinking wildly, he wrote the answers on the blackboard according to the thought of solving the problem in his mind. Professor Li Xuesong, who was standing beside him, looked silly.

If it's scribbled, it's all right. At most, after this guy has finished writing, he'll laugh beside him... Oh no, criticize education.

But this guy wrote it, and he couldn't find out the fault at all!

I even feel that

There seems to be a little bit of truth?!

Especially when Hao Yun wrote line 4, his whole face changed.

what the fuck!?

How could this problem be solved?

He was shocked not only by himself, but also by He Ping standing under the stage.

Staring at the blackboard, his eyes were straight, and he could not help murmuring.

"To the contrary? It's a counter argument?! It's impossible. I've tried to disprove it before

"I see... I see... I see..."

Sitting next to him, Zhou Xuan and Prince Yu looked at each other and exchanged a confused sight.

Zheng Xueqian, sitting in the back row, swallowed his saliva, and his nervous pen was almost crushed.

It's not to cheer for Hao Yun, but I didn't expect that the guy who sleeps diagonally is so powerful!

Careless

Zhu Kening and Liang Ziyuan didn't have any special reaction. One of them was not interested at all, and the other didn't understand. They just felt that they were a bit bullish.

The whole 1801 and 1802 classes were silent.

Whether it's real Xueba or fake xuezha, looking at the process of writing on the blackboard, almost everyone is stunned.

He didn't pay attention to the expressions on the faces behind him. He completely focused on Hao Yun on the blackboard and felt that he was entering an unprecedented state.

How to put it?

It's like the whole world is slowing down.

Only his thinking continues to accelerate

Is it because of math mastery?

It turns out that this is the effect of qualitative change caused by quantitative change

Although his intuition tells him that the accelerated thinking can be faster and further developed, until he finally touches the so-called realm of God! But for him at this moment, even this degree of acceleration is completely enough.

What is in front of you is just a written topic, far from being creative.

A little insight gradually rose in my heart.

Until this moment, Hao Yun finally understood what kind of existence this so-called system of extraterrestrial talents was.

The clock on the wall is walking second by second.

After almost three turns, he stopped his chalk and looked at Lao Li standing beside him.

"... I'm done."

I don't know if I didn't hear what I said. Professor Li Xuesong didn't have any reaction. He didn't even move his eyebrows.

In order to make sure that the old man was not asleep, Hao Yun politely asked.

"What's wrong with the procedure?"

Hearing this inquiry, Professor Li Xuesong finally recovered.

He looked straight at Hao Yun, then looked at the blackboard, shook his head and his stiff neck like a nod, and spat out a sentence from his mouth.

"No problem..."

Hearing this, the stone hanging in Hao Yun's heart finally fell to the ground.

It is worthy of Jiangda.

It's true, some cattle!

In the past, I had to put it on the IMO competition to give people a lot of problems. In this life, I only need to think after class about the first lesson of senior mathematics.

A wave of pressure arises spontaneously. Hao Yun is also embarrassed to ask the professor if he really doesn't need to come in the future. After saying "then I'll go down", he sneaks down the platform quietly.

The whole classroom was silent.

I don't know who started, but I clapped.

He Ping sat back with his eyes straight. He didn't know what he was talking about.

Back in the last row, Hao Yun always felt that there seemed to be a lot of people watching him around, which made him feel uncomfortable for a long time.

Fortunately, the applause lasted only a short time.

As Professor Li Xuesong returned to the platform without saying a word, the students in the classroom also re entered the state, seriously staring at the blackboard, ready to listen.

"The answer is the same as what this classmate wrote. Basically, it's a standard answer... You copy it. If you don't have time to copy it, take a picture. If you don't ask him, I won't tell you the details."

"Now turn to page 12, and we'll continue what we talked about in the last lesson..."

I don't know if I was stimulated. In the second half of the class, Professor Li Xuesong didn't repeatedly nag such difficult words as "today's young people" and "how old men we used to be".

However, I don't know if it is my own illusion. Hao Yun always feels that he is a little absent-minded standing on the platform?

Or I'm out of my mind.

Thinking of this, Hao Yun can't help but worry. Is his late behavior making him angry?

But shouldn't it?

People are not saints, who can do nothing wrong, not to mention their own just late, the wrong also admit, a correct attitude! If this can still be angry, it's too careful, isn't it?

And Zheng Xueqian

This guy always looks back at himself in class, which makes Hao yunqi embarrassed.

The bell rang at last.

Professor Li Xuesong left without saying a word.

Everyone thought that he was going to solve the internal emergency, but unexpectedly, five minutes later, after the bell rang, a little brother of a doctoral student came.

Look at the hair style handed down from generation to generation, it's his students who can't be wrong.

Sure enough, his opening remarks also confirmed the big guys' conjecture.

"There is something wrong with Professor Li Xuesong. I will teach you the second half of the class."

Looking at xiaomengxin in the classroom, he smiles. The doctor picks up the textbook on the desk and scratches the back of his head.

"Er, just now the professor left in a hurry..."

"Who can get up and tell me what he said just now?"