"You should be more open-minded. If you are late, you will be late. Can't you walk in through the front door openly?"

Damn!

I'm not afraid of disturbing you in class.

Isn’t it international practice to be late to enter through the back door?

Yishuang looked over, even though his face was quite thick, Hao Yun was 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 stern face.

“Where is the homework?”

Do, homework?

When Hao Yun heard this, he suddenly felt embarrassed.

"Uh, forgot to bring it."

Forgot to bring it?

hehe!

If you don’t write, you don’t write, and you still find such low-level excuses.

Looking at Hao Yun with a smile, Li Xuesong continued, "Forgot to bring it? That's OK, you mean to write it? Anyway, there's only one question, so you can write it now, right?"

As he said that, he tapped the blackboard with his index finger.

“Come here to write.”

Hearing the old professor's words, a commotion sound spread in the class, and many people whispered.

Hao Yun, who was standing in the back row, couldn't hear what they were talking about. He just wanted to complain about the old professor's nerves today. He didn't do anything that hurt the world. He was just a minute or two late, so why is it so difficult?

Looking at Lao Li's smiling expression, he knew that he was destined to escape this disaster today.

In his heart, Hao Yun sighed and finally walked towards the podium.

When passing by the front row, he noticed that Zheng Xueqian was frantically shook his eyes and handing over the words, and poked the screen of his phone hard, as if signaling him to look at WeChat.

[You are crazy?! You are really coming up? No one can write that question!]

Although I could guess that this good brother probably sent the answer to his homework to himself, he had already walked here, and he obviously had no chance to take out his phone.

Hao Yun returned his reassured look and communicated with his eyes.

【Don't worry, I'm fine.】

When faced with that "confident" look, Zheng Xueqian was stunned for a moment.

Damn?

What does this guy mean?

Could it be...it was really written out?

It's impossible!

A question that He Shen didn't even write...

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

After taking the chalk from Lao Li, Hao Yun stood in front of the blackboard for a while, and suddenly turned around with a little embarrassed look.

"Uh, what's the question...I didn't memorize it."

When Li Xuesong heard this, he immediately smiled and said to see when you acted, pointing at the podium with his chin.

"There are so many on the podium, just copy it."

It's okay to copy one...

Are you not afraid that I will see the answer?

Hao Yun, who picked up the homework at the top, muttered a few words in his heart, but after just a second of his opening, he was stunned for a moment.

Good guy, I wrote a "solve".

Isn't you going to have to settle it regularly?

At least hide the book below!

When I looked at the name again, it was actually Liang Ziyuan's.

After silently recording the question, Hao Yun helped him to put his homework book at the bottom.

Taking all the student's small movements, Li Xuesong laughed and didn't expose them. He just raised his eyebrows and continued to say.

"Now you know the question?"

"Uh, I remembered it."

"Remember it? OK, then don't talk nonsense, hurry up and start writing!"

It was not a particularly difficult question at first, and even there were only a few letters that appeared. All the information in the question could be explained in two sentences.

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

However, this copy doesn't matter.

When he finished copying the topic and read it again, he was stunned.

[Suppose the positive integer a and b satisfy (a2+b2)/(ab+1)=k∈N, prove that k is the square of a certain positive integer.]

Good guy.

This question...

It looks familiar?

Seeing that Hao Yun didn't move for a long time, Li Xuesong thought he couldn't do it, so he smiled and joked: "If you can write it out, you won't have to take my class in the future, and you will give all the credits."

Hao Yun swallowed and asked incredible.

"……real?"

"Ha, I need to lie to you?"

Then I really wrote it...

Confirm that this guy didn't seem to be talking sarcastic, Hao Yun hesitated for a moment, and finally put the chalk on the blackboard and started to write.

[Suppose k is not the square of a positive integer, then a≠b.]

[Considering the indefinite equation a2-kab+(b2-k)=0, if a=b, k=1 can be deduced, so it is inconsistent with the assumption.]

[So it is better to set a)b)0, take a set of solutions (a0,b0), so that a0+b0 is minimized...]

Although I copied this question in the draft book before, Hao Yun had never taken the time to read it carefully, otherwise he would not have been surprised here.

And the reason why I am surprised is also very simple.

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

As for why he knew...

It’s not because he participated in that competition, but because just yesterday, he saw it in the high-math textbook full of notes, and finally did it himself.

He even remembered that this question was copied in the blank space at the end of the page of Vedic's theorem.

According to the slightly joking comment from Professor Lu, no one in the main test committee made this seemingly simple number theory issue back then. Finally, he asked four number theory experts in Australia, the host of the competition, and was at a loss for a while.

Since experts cannot solve this question within the specified time, this question has become a legend.

There were hundreds of contestants in total, and only a dozen contestants finally wrote the answers, one of them even received a special award from the competition's main test committee for their beautiful answers.

At this moment, the solution he wrote on the blackboard was the "Bid Answer" that was awarded the special prize that year.

What is very interesting is that according to Professor Lu's writing, these dozen contestants who wrote the answers eventually became famous figures in the mathematics community. When commenting on this little-known past, the professor also wrote with emotion—

[Usually, mathematics is the product of intuition, but some counterintuitive propositions are not ruled out. Just as our common sense always tells us that counter-proof is unreliable, our common sense occasionally deceives ourselves with anomalous sense.]

[It just surprised me a little. Even Tao Zhexuan, who should not lose to this question, was unfortunately caught in its hands.]

Although he had no particular interest in mathematics and Hao Yun had never heard of the names mentioned by the professor, he still came to a reliable conclusion from the limited comments.

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

Thinking of this, I suddenly felt like a holy relic.

The only shame is that after he finished reading the notes, the system did not leave him a little dust, and directly erased the existence of the thing from this world.

Just as Hao Yun was thinking about it and writing the answers on the blackboard according to his impression of problem-solving ideas, Professor Li Xuesong, who was standing next to him, was stunned.

It would be fine if it was written randomly. At most, after this guy finished writing, he would laugh at him... Oh no, criticize and educate him.

But this guy wrote it, he couldn't find any problem!

Even think...

It seems that there is some reason?!

Especially when Hao Yun wrote the fourth line, his whole face changed.
To be continued...