Xueba, I beg you to go and escort him quickly!

Yang Kaixuan, "Hey..."

After a sigh.

Yang Kaixuan continued to listen to the class.

Except for math class, Yang Kaixuan listened selectively to other subjects.

But when it comes to math class, which is his home game, he doesn't listen to the class anymore, and is doing his own Mathematical Olympiad problems seriously.

This is a new set of books.

After Yang Kaixuan analyzed Xu Heng's problem-solving ideas, he also began to gradually get used to it.

设等差数列{An}满足3A8=5A13，切A1＞0，Sn为其前n项之和，则Sn（n∈N*）中最大的是……

In the Mathematical Olympiad, this is a multiple-choice question, but in the normal exam, it can be a calculation question, which many students still can't do.

Look again!

It is known that a and β are acute angles, sina=x, cosβ=y, cos(a+β)=-3/5, what is the functional relationship between y and x?

This is also a multiple choice question.

Compared with ordinary test papers, even the high-level test papers are much more difficult.

Moreover, among other questions, even if the question types are similar, the difficulty of the data is increased, or the question types are changed.

If the difficulty of the general exam is the easy mode, and the college entrance examination is the general mode, then this Mathematical Olympiad competition is the nightmare hell mode!

The most difficult!

Yang Kaixuan answered the question as if he had nothing to say.

In the triangle ABC, it is known that tanB=3 under the root sign, sinC=(2 under the root of 2)/3, AC=3 under the root of 6, what is the area of ​​the triangle ABC...

Are these questioners out of their minds?

Find the area?

The corners of Yang Kaixuan's eyes twitched violently, and his scalp was numb.

But he still bites the bullet and goes on...

Step by step, slowly answer.

Xu Heng saw it and smiled, he had seen this question before, it was exactly the same, and the answer was ready to come out.

But with Yang Kaixuan's problem-solving ideas, it is obviously complicated.

But this guy doesn't ask himself what he has to say, so let's play his own game with peace of mind.

Xiaokang has not found himself recently.

Xu Heng had a great time.

winning streak all the time...

After saving enough money, Xu Heng went to buy new heroes.

Playing around, Xu Heng found out that King of Kings also has something similar to LOL Genting, called King of Simulated Battles.

He is interested.

Tried a few to get started.

"It's similar to Genting mode, but it's also very simple, so let's play it."

Xu Heng learned a little bit, and did some research on the Internet.

It is said that the talent of the demon seed is very strong, and the heat is also very high.

The six heroes not only increase attack speed collectively, but also absorb physical and magic blood, as well as armor!

But the chance of this talent appearing is very low.

If talent doesn't come out, it's basically useless.

He will be nicknamed Mo Lao Ba.

Eight people play chess on the chessboard. If you have no talent, you are No.8.

Xu Heng smiled, "This is the only way to be challenging, and it's worth playing."

In the first game, luckily, the magic seed talent came!

Look at everything!

No matter what mage lineup or assassin lineup, they are all in seconds!

Easy first!

In the second game, it was still the same.

The third game, here we go again.

Xu Heng frowned, "This is too different from what is said on the Internet! I have done it three times in a row, and I will stop playing!"

How did he know that in order to play a game of demon talent, others begged his grandpa to sue his grandma, and he was almost sacrificing that he had been single for 30 years!

After quitting the game, Xu Heng also began to feel bored.

"Let's find a few questions to brush up..."

Yang Kaixuan, who pricked up his ears, stared at Xu Heng.

Xu Heng searched for questions on his phone.

Swish swish!

Suddenly, he stopped.

Yang Kaixuan stretched his neck to look over.

Title: Let f be a mapping from the set {1,2,...,n} to itself, define f(A)={b丨彐a∈A, f(a)=b} for the non-empty subset A, if If f(A)=A is satisfied, then A is called a subset. Prove that there are exactly an odd number of fixed subsets.

Yang Kaixuan is confused!

The math teacher Xue Laiyun who happened to pass by was also confused.

He and Yang Kaixuan glanced at each other.

Yang Kaixuan seemed to ask again in his eyes, "Teacher, can you?"

Xue Laiyun left quickly.

If you don't leave, is it possible that you still have to wait for embarrassment?

Xue Laiyun fled in obvious desperation.

Yang Kaixuan was speechless, and his eyes returned to Xu Heng.

But Xu Heng didn't intend to do this question.

Not even a pen!

But he read this question, and after a while, he brushed it away.

[True] Brush up on the questions!

Just swipe it, turn the page on the phone, and this question is over!

Yang Kaixuan, "???"

He never expected that Xu Heng would brush it over in a flash!

If it was on someone else, Yang Kaixuan would definitely think that he wouldn't, but this happened to be Xu Heng again!

The most reliable thing is that Xu Heng looked at this question as too simple!

That's right!

It's just too easy!

Yang Kaixuan, "Xu Heng, do you still think this question is easy?"

Xu Heng looked over, "It's okay!"

Yang Kaixuan curled his lips, and was about to ask how to do it, but he shut up.

This is seriously beyond the standard for him!

He could only ask, "How did you find this question?"

Xu Heng, "I searched the proof questions of the Department of Mathematics of Tsinghua University and Peking University, and I found it."

"!!!"

Yang Kaixuan really wanted to slap himself in the face.

Why the fuck are you asking this.

Xu Heng looked at Yang Kaixuan's strange expression, "?"

"Don't think I know everything, I also..."

Yang Kaixuan said excitedly, "Don't tell me you don't know this question?"

"No, no, I can answer this question. It's so simple, who wouldn't... um... No, you will be able to when you go to college."

Yang Kaixuan had black lines on his face.

He stopped asking!

I don't even look at Xu Heng anymore!

He has to do his own test paper seriously.

But still couldn't help but glance at Xu Heng.

Xu Heng has been searching for topics on this side.

But none of them started writing.

A few times when Yang Kaixuan picked up a pen, he became excited. Did he find a problem?

But within a few seconds, Xu Heng shook his head and put down the pen again.

After about ten minutes, Xu Heng's straw paper was still white.

"Is there no question that can be difficult for this guy?"

Just wondering, the get out of class bell rang.

Xu Heng put down his phone, and said to Yue Pingting, "I put my phone here, show it to me, and I'll go to the bathroom."

Yue Pingting, "Yeah!"

At this time, Yang Kaixuan stood up and looked at the question on Xu Heng's screen.

设二次型f（x1，x2，x3）=2（a1x1+a2x2+a3x3）2+（b1x1+b2x2+b3x3）2，记……

……

Yang Kaixuan's scalp was numb, and he looked at Yue Pingting, "Yue Pingting, can I look at this question on Xu Heng's phone? Just two seconds!"

Yue Pingting nodded.

This is far beyond Yang Kaixuan's cognition, he wants to see how Xu Heng found such a topic!

What secondary type?

What proves the correspondence matrix?

What unit vector?

What standard form?

When he got the phone and tapped the screen, the search box popped up.

above:

"The real exam questions for the Mathematics Department..."

And there is a word "difficult" at the end!

Xu Heng is searching for real questions for the university entrance examination!

And it's even harder!