Chapter 14 – Lagrange’s Mean Value Theorem

Police station, communication room.

The police and Song Yu stared at each other.

The policeman held a pen and gave a smile that wasn’t really a smile, “Why is it you again.”

Song Yu took his time replying, “Probably because I was born with a strong sense of responsibility and like to call the police when I encounter unfair things.”

The policeman was amused, “That’s not it. What I’m asking is, why are you always the one getting beaten up.”

Song Yu: “……”

Xie Sui laughed out loud next to him.

The gangsters had actually suffered more injuries than they had, but Red Hair and his group had records in the police station, having committed countless previous criminal offenses. The police considered their attacks to be self-defense and simply took their statements before letting them go. Originally, they’d wanted to contact their parents, but Song Yu took the initiative to tell them about Xie Sui’s family situation. His words were reasonable and moving, and were enough to convince the police to skip over this part of the process.

It was the same police station, followed by a visit to the same small clinic.

There were only a few people in the brightly lit clinic.

The male doctor in the clinic still had an impression of them.

The doctor: “Last time it was a leg injury, and this time it’s a hand injury. You’re even fighting with real knives. Young man, you’re quite wild.”

Xie Sui sat in the chair. His eyes curved slightly and he smiled as he spoke modestly, “So-so.”

The doctor was so angered by this that he almost broke the pen that he was using to write, “You’re proud that I said you’re wild? While you’re showing off your prestige outside, have you thought about how your family is worrying about you? When you’re this young, you should behave and study. Why insist on following a crowd of young gangsters who don’t have proper jobs? If something happens, the ones who’ll end up distressed will be your parents.”

Song Yu sucked on his mints and spoke up for Xie Sui, “Uncle, you’re misunderstanding him. You can’t just look at the surface.”

The doctor rolled his eyes at him, “I haven’t even started on you yet. You’re his friend, right? So you just watched from the side as he fought? Didn’t you try to stop him?”

Song Yu choked. There was a hint of embarrassment on his face as he scratched his head, “We’re not talking about the same thing.”

The doctor placed the medicine into a bag and sneered, “Fine. Then I won’t look at the surface. Could it be that your wounds are from fighting against aliens? Do aliens also use such earthly, cold, steel weapons too?”

Song Yu: “……”

The TV on the wall was currently showing Degas Altman. The doctor’s two year old son heard them, clapping his hands as he turned his head. His big, clear eyes were curved up happily as he smiled and laughed like a baby, “Aileeans.”

Xie Sui paid for the medicine and picked it up, “Thank you.”

The doctor was hating iron for not being steel, “In the future, when my son grows up, if he ends up like you and gets hurt all day long, I’ll break his leg first.”

Song Yu chewed on his candy and complained, “I already said, don’t look at the surface. Uncle, what’s the matter with you! My friend got hurt while dealing with tyranny. He fought on his own against a hundred, bravely going up against street bullies. He protected the personal and property safety of all the junior high students across the whole of Lianyun Street. These wounds are all a hero’s scars.”

The doctor: “……”

The child sitting in the chair drooled and clapped again, “Hero.”

Song Yu was amused, “Ah, this little child is so smart. Say it again.”

The child, who was just praised, laughed sweetly and said in a baby voice, “Big brother, hero.”

The doctor saw that he was leading his old child astray and was so angry that he drove them out with a feather duster, “Leave, leave, leave, go and fight bravely against street bullies. I think that, in fact, you’re the biggest bully in Lianyun Street.”

“Ahahaha––”

Song Yu, who’d been promoted to a street bully, couldn’t stop laughing as he pulled Xie Sui with him and left.

A few moths were gathered around the street lamp outside the clinic. On this quiet summer night, insects whispered from the bushes.

It was already very late. Song Yu stood under the streetlamp and called Uncle Ma to come and pick him up at the same place as before.

After hanging up the phone, Song Yu turned to Xie Sui and said, “I won’t come over much in the future. See you at school after summer vacation.”

Those gangsters had a criminal record. This time, they’d probably have to stay at the station for a good many days, meaning Xie Sui should be safe for July and August.

He’d solved the most dangerous thing he’d encounter during this summer vacation.

Song Yu felt that there was no need to run over here again.

Xie Sui’s nose could still smell the scent of mint.

He couldn’t help but wonder exactly how much Song Yu liked mint.

His fingers curled and he smiled slightly, “Mm. See you when school starts.”

Song Yu stared at him, thinking about how the teenager had fought so fiercely in the deep alleyway, and his words were momentarily stuck in his throat.

For an instant, he felt that he didn’t understand Xie Sui anymore. But then, it seemed that he had never really understood Xie Sui.

He got into the car and left the remote residential area, heading to the downtown area.

The neon lights shone brightly onto Song Yu’s thoughtful face.

Uncle Ma asked, “Young Master, did you come to see your friend who felt like a good friend at first sight again?”

Song Yu came back to his senses, “Yeah.”

Uncle Ma said, “The old Madame is getting suspicious about you running off every day. I think, if you come a few more times, she’ll want to meet this classmate of yours.”

Song Yu started laughing, “I won’t come anymore.”

In fact, it was no big deal for Grandma Meng to meet Xie Sui.

However, he’d promised 008 that he wouldn’t appear in front of Xie Sui as the Third Young Master of the Song Family. Later, he planned to make up an identity as a ‘poor, distant relative of the Meng Family’, but it would be easy for his real identity to be exposed in front of Grandma Meng.

*

Song Yu’s QQ account had very few friends on it. He lay in bed playing with his cell phone, looked at that full stop-kun’s black profile image, and his hands inexplicably felt a little itchy, wanting to send a message.

However, he’d racked his brains to think up negative reviews that day and then run through the street in the middle of the night afterwards. He was tired both mentally and physically.

At some point, he fell asleep.

When he got up the next day, it was already 9 o’clock in the morning.

When he went downstairs for breakfast, Song Yu received a bombardment of messages from Ma Xiaoding.

[ Sadako Won’t Forget Those Who Dug The Well: Ahahahahahahahahaha ] 

[ Sadako Won’t Forget Those Who Dug The Well: Brother Yu, were you the one who gave negative reviews like crazy? I went to their restaurant to eat on purpose today and saw Zhu Zhixing’s mother’s green face. She’s probably dying of anger. ] 

[ Sadako Won’t Forget Those Who Dug The Well: Ahahaha, too genius! I also asked my fellow brothers to follow your footsteps and do a few negative reviews. Let’s anger this vicious woman to death! ] 

Song Yu was already too lazy to care about Zhu Zhixing’s affairs. When he thought about Grandma Meng’s expectant gaze and the stack of exam papers on the table, he instantly had a headache.

He sipped at his milk and sent Ma Xiaoding a message.

[ Your Husband, Brother Yu: How are your grades? ] 

[ Sadako Won’t Forget Those Who Dug The Well: ??? ] 

[ Sadako Won’t Forget Those Who Dug The Well: Why are you asking about this, they’re okay… kinda. ] 

Anyone who could be admitted into Jingcheng No.1 High School had to have decent grades.

Song Yu curled his lips briefly and began to type.

[ Your Husband, Brother Yu: Having good grades in junior high doesn’t necessarily mean you’ll have good grades in high school. Don’t think that you can relax over summer vacation after the high school entrance exam is over. Others are enrolling into cram schools like crazy. There’s a lot of competitive pressure in No. 1 High School and there’s always someone wanting to jump off a building every year. The fact that it hasn’t been sealed for inspection by the government is really due to luck. You can’t lose at the starting line in the first year. ] 

Ma Xiaoding was shocked by this speech that sounded so much like his father.

[ Sadako Won’t Forget Those Who Dug The Well: … Brother Yu, what are you trying to say. ] 

Song Yu had already returned to his room, pulled out his chair, and sat down at his desk. He was staring at the exam papers that were piled up like mountains in front of him.

[ Your Husband, Brother Yu: Come to my place and I’ll share some knowledge with you. Fellow brother, let’s do exam papers together. ] 

[ Sadako Won’t Forget Those Who Dug The Well: …… ] 

Can we not be fellow brothers anymore.

After giving half the exam papers to Ma Xiaoding, Song Yu felt much more comfortable.

His Grandma Meng had given him a lot of materials. At the start of the transition period, much of the information was a consolidation review of junior high, followed by some introductory exploration into high school knowledge. There were even original questions from college entrance examinations, just so that he could have a grasp on the level of difficulty.

Except for that first exam paper he did, Song Yu didn’t actually plan to simply pound at it with his head. As he went on, he slowly started to find the feel for it.

He pulled out a paper from the bottom of the stack that had a very high level of difficulty and wasn’t required to be complete. Song Yu casually flipped to the last question and froze.

It was a very classic function problem. E to the power of X and E times X.

He currently didn’t intend to try this final question, but he felt that it was vaguely familiar and a very vague concept even appeared in his head. After thinking about it for a long time, he finally remembered it.

Wasn’t this a typical example of Lagrange’s mean value theorem?!

The reason why he still remembered this problem was probably related to the name of the theorem when his high school teachers mentioned it. The name of the theorem was too strange.

The theorem given by Baidu didn’t provide any specific examples and was very difficult to understand. It just happened that Song Yu wanted to initiate the first conversation with Xie Sui.

So he took a picture of the question and sent him a message.

For the sake of getting the first kill for the disgrace of the original A66, he gnawed on his pen and thought it over.

He pretended to be profound.

[ Do you know what Lagrange’s mean value theorem is? ] 

*

Xie Sui was lying on the bed, his fingers tapping on the computer keyboard as he invaded the Linshui intranet and called up the surveillance records.

After he finished everything, he went to pick up the water cup nearby and caught a glimpse of the message on his cell phone.

[ Song Yu: Do you know what Lagrange’s mean value theorem is? ] 

Xie Sui: “……”

He should be glad that he hadn’t started drinking yet.

As a student, Xie Sui had always been outstanding. He was lonely and indifferent and never had any contact with normal students.

Therefore, he couldn’t understand Song Yu’s brain circuits, which seemed to rely on perseverance when solving problems.

––You even have to rely on counting for your permutations and combinations. Why would you ask about Lagrange?

Of course, Xie Sui didn’t ask such a question that would hurt his self esteem out loud. This was because he could see that Song Yu’s enthusiasm for learning seemed to be very high, and he didn’t want to attack it.

Xie Sui took out a pen and a piece of paper, considered Song Yu’s knowledge reserves, wrote down the standard solution to the problem in detail, then took a photo of the paper and sent it over.

[ Xie Sui: [image] ] 

[ Xie Sui: You don’t need that. ] 

Song Yu waited for a long time, only to receive this sentence, followed by a photo that showed clear and logical thinking, as well as beautiful handwriting.

It was even easier to understand than the answer.

Amazing. He was really worthy of being the protagonist, the favored son of heaven.

However, Song Yu felt like he was already on top of the bull’s horn and couldn’t get off. He persevered and continued to ask.

[ Song Yu: So, how do you solve it with that one? ] 

He sent out some emoticons while he was at it.

[ [head scratching with question marks] ] 

[ [begging you] ] 

Xie Sui’s fingers paused for a moment over the small soybean that was scratching its head. It was as though he could see Song Yu’s troubled expression on the other side of the cell phone; his gaze grew distracted, and his thin lips curved slightly.

[ Xie Sui: You really want to know? ] 

[ Song Yu: Of course. ] 

[ Xie Sui: Cross out the entire section from the third line to the fifth line and change it into ‘insert Lagrange’s Mean Value Theorem’. ] 

“???”

After Song Yu did it according to his instructions, he really experienced how it felt to be a ‘learning scum’.

[ Song Yu: There’s a number in the interval that makes them equal. ] 

Xie Sui didn’t want to tell him that it was the theorem. After thinking about it, his eyelashes swept down, a bit of dark amusement flashing in his dark pupils.

[ Xie Sui: Didn’t I give you an interval? You can try them one by one and you’ll eventually find it. ] 

Song Yu: “……”

Song Yu: “………………”

Your damned intervals were infinite!

Why did he always have the feeling that Xie Sui was secretly laughing at him?