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Chapter 51 The end of the preliminaries
Qiao Yu didn't want to get a very good result in the preliminaries. He would be satisfied as long as he passed the line, because according to the rules of the competition, the preliminary results had nothing to do with the final results.

But when the time came and he opened the question bank, Qiao Yu smiled.

For example, the first question belongs to the category of combinatorial geometry. It tests plane geometry, combinatorial mathematics, visibility diagrams, etc. The question mentions the problem of line of sight obstruction. According to Qiao Yu's understanding of mathematics, this kind of problem usually appears in computational geometry.

But this is a multiple-choice question.

Qiao Yu is not bragging, what he is best at is answering multiple-choice questions.

He didn't even have to draw a picture. Just based on the pre-arrangement of the points and visibility issues, he deduced that the number of people could not be more than 6, eliminating answer D.

Since towers E and F are out of sight, all that's left to do is draw a picture in your mind based on the conditions.

The final answer was exactly six people.

It took ten minutes and feeling very good, Qiao Yu looked at the second question, which consisted of two multiple-choice questions.

Coincidentally, this question examines probability theory and expected value.

It happened to be a field he was familiar with. The mathematical idea needed for the first question was probably the memorylessness of exponential distribution. In layman's terms, the probability of an event happening in the future has nothing to do with the past.

In short, I have learned it, it’s simple.

When it came to the third question, Qiao Yu finally felt that it was starting to get difficult.

However, this question tested the contents of algebraic number theory and geometric number theory, combining eigenvalues ​​with number theory. Qiao Yu finally understood the significance of open-book exams. He had a vague impression of the discussion of the density of grid points in the plane, but he was not sure.

So Qiao Yu started searching online according to the prompts below the question, and soon found the famous Minkowski theorem. Then he began to look for various explanations of geometric number theory on video websites, marked them, and collected them directly.

However, Qiao Yu did not watch those videos for the time being. Instead, he gave up the third question and started studying the following questions.

It's just a preliminary round. It's enough to enter the finals. According to previous years' experience, you don't need to finish all the questions.

In this way, Qiao Yu sat in front of the computer answering questions throughout the entire Saturday, except when Qiao Xi called him to eat.

Xia Keke came to see Qiao Yu once in the evening as usual, but after learning that Qiao Yu was participating in an online math competition, she did not knock on the door to disturb him.

There were seven questions in total. By the time Qiao Yu felt dizzy and went to wash up and sleep, he had completely answered three questions: the first, second, and fourth.

The fourth question was about linear algebra and abstract algebra, and mainly tested the analysis of eigenvalue decomposition and eigenspace structure. Qiao Yu was extremely strong in this area, and similar preliminary questions could not stump him at all, not to mention that he had strengthened his study of algebra and number theory during this period.

For the other four questions, Qiao Yu was not very confident, or had only a rough idea, so he decided to wait until the next day to watch the video and then selectively answer two questions.

According to the experiences shared by finalists from previous years’ preliminary rounds at the forum, basically as long as you have the confidence to answer four questions correctly, you will basically get a ticket to the finals.

Of course, to be on the safe side, Qiao Yu decided to answer at least three or four questions tomorrow. He didn't need to get it all right, but if he could get some general ideas across, he should be able to get some points.

Another reason why I didn’t rush to take action today is that any operation on the Internet will leave traces.

Especially when using someone else's backend and doing a few questions a day, it's easier to be lost in the crowd. There's no need to show anything special in the preliminaries, since there's no money for them. After all, he's only 15 years old, and there's almost no threshold for Alibaba's math competition. This means that as long as you're strong enough and don't fear embarrassment, math professors from top universities and even Fields Medal winners can sign up to participate.

And he was just a little Karami who was a little over fifteen years old.

If you perform too well and get noticed, you might be put under the spotlight for observation.

Qiao Yu didn't really mind being famous, but according to this year's competition schedule, the results would be announced at the end of June, so the contestants would have a little time to prepare before the finals began in early July. Being watched and talked about during this period, and not getting paid, was just asking for trouble.

To put it bluntly, the focus is still the final.

The next morning at six o'clock, Qiao Yu got up from his bed. He started watching the videos he had collected and marked online the previous day. He spent the whole morning studying. Qiao Xi brought his meals to his room.

It was not until two o'clock in the afternoon that Qiao Yu started answering questions again. At eleven o'clock in the evening, with nine hours left before the end of the competition, he had finished all the questions.

It could have been earlier, but Xiaolibaba's online answering system is not that easy to use.
Having overcome this small difficulty, Qiao Yu is still very confident of making it to the finals.

……

Monday was the Dragon Boat Festival, so there was a day off, but Ranjie still got up early in the morning, turned on his computer at 8 o'clock and started to look at the question bank of the Xiaolibaba World Mathematics Competition.

According to the practice in previous years, whether it is the preliminaries or the finals, Xiaolibaba will publish the questions and answers in the history question bank on the official website simultaneously after the competition is over.

Although teachers for the Mathematical Olympiad do not need to study this type of competition questions and he has not signed up for the competition, Ranger pays attention to it every year because the questions in the Xiaolibababa Mathematical Competition are very interesting.

For those who have no interest in mathematics, it is probably difficult to understand the sense of satisfaction after solving a difficult problem. Not to mention that Qiao Yu may have also signed up for this year's competition. Lang Jie has always been curious about Qiao Yu's mathematical level.

Combining the difficulty of the questions with Qiao Yu's final score, you can probably get a rough idea of ​​the result.

The arrangement of the preliminary round this year was good. After the exam, it was the Dragon Boat Festival break. As an older single man with no other hobbies, he could use the time to study the test questions.

After reading it roughly once, Langjie had a rough idea in his mind. The difficulty was basically the same as in previous years, and it was probably at a medium-high level in the mathematics community. The scope was also very wide, involving algebra, geometry, number theory, combinatorial mathematics, and probability.

This question setting mode is more friendly to contestants who have a background in mathematics, after all, these contestants have a relatively systematic learning experience. It is indeed more difficult for non-professional contestants.

Especially the last question, which not only involves the modeling and solving of differential equations, but also includes the analysis of dynamical systems and the understanding and reasoning of periodic motion. If he were to do this question, it might take him a whole day and he might not get it right.

As for Qiao Yu's words...

When the image of this child appeared in his mind and he thought of his pious attitude when he asked whether the prize money needed to be taxed, Ranjie was not sure whether this kid could pass the preliminaries.

What a pity. I have a day off today, so the Olympiad class in the afternoon has naturally been cancelled.

However, his curiosity could not be suppressed and he picked up his phone and opened WeChat.

　Thanks to the book friend, Fengchenyun1 for the reward

　　
　
(End of this chapter)