My subject turned into a beautiful girl

"Wonderful, wonderful~"

In the following classes, An Yi kept cramming on the questions that her older brother kept sending her, and would occasionally exclaim that she had "gotten some good stuff".

"What's so clever about it?"

Wang Xinze, who sat next to Wang Xinze, couldn't resist and leaned closer, but quickly shrank back in fear.

"What the hell are these things? I think I've seen a letter written by President K!"

"You're exaggerating. We can't even understand those Heaven-rank techniques at our current stage. The questions on this paper can be solved with at most a second-grade Human-rank technique."

An Yi shook his head and explained.

"Although we are learning a third-grade Human Rank technique, with our spiritual roots and aptitude, as long as we calm down and study carefully, we can actually learn it—it's just a second-grade Human Rank technique. At most, we'll need to spend a little more time!"

"Really? I don't believe it."

Wang Xinze expressed his doubt, pointing casually, "Then explain this problem to me?"

「设正实数a，b，c满足a²+4b²+9c²=4b+12c-2，求1/a+2/b+3/c的最小值……这道？」

An Yi pointed to the question.

"Yes, this is one of those classic questions. I can understand each Chinese and English word individually, but when put together, it becomes something I can't even begin to grasp!"

Wang Xinze nodded, "I have absolutely no idea how to solve this!"

"That's because you haven't learned the advanced second-grade cultivation technique yet. It won't be difficult after you learn it."

An Yi pulled out a blank sheet of scratch paper. "We've all learned about Cauchy's inequality, you must remember it, right?"

"..."

The two stared at each other silently for two seconds.

"Um, this is the formula."

An Yi paused for a moment, then wrote down the inequality (a²+b²)(c²+d²)≥(ac+bd)² on the paper.

"You must... at least have some recollection of it!"

"Oh, you mean this? I know that, it's the equality condition if and only if ad = bc!"

Wang Xinze suddenly realized, "So this is called Cauchy's inequality? I always only remember the formulas, not the names... But what does this inequality have to do with this problem? Doesn't this problem also have 'c'? There are three unknowns, right?"

"Yes, that's why I said before, it's because you haven't learned the advanced second-grade techniques yet. The Cauchy inequality we're learning now is third-grade, and we've only learned the binary algebraic form. The next level up corresponds to the human-grade second-grade technique, the ternary Cauchy inequality!"

An Yi wrote on the paper while explaining.

The standard formula for the ternary Cauchy inequality states that for any real numbers a₁a₂a₃ and b₁b₂b₃, (a₁²+a₂²+a₃²)(b₁²+b₂²+b₃²)≥(a₁b₁+a₂b₂+a₃b₃)², and equality holds only if a₁/b₁=a₂/b₂=a₃/b₃.

The corresponding fractional form after transformation is a₁²/b₁ + a₂²/b₂ + a₃²/b₃ ≥ (a₁ + a₂ + a₃)²/(b₁ + b₂ + b₃)... See? After seeing this formula, doesn't the problem seem less daunting now?

"No, no, no, I think your understanding is clearly different from mine. I'm already dizzy just looking at this formula!" Wang Xinze shook his head like a rattle drum.

"How could that be?"

An Yi blinked, then looked at the formula she had written down, making sure she hadn't made a mistake. "This formula looks so elegant, it tastes delicious!"

"It's okay, I think I understand... You've read Cthulhu novels, right? There's a concept in them called clairvoyance. Different types of clairvoyance can lead to different understandings of the same thing."

Wang Xinze sighed.

"My spiritual vision is low; what I see is a tangled mess of octopus tentacles. Your spiritual vision is high; what you see is a delicious dish. So, you'll be very happy and joyful eating this dish, while I not only can't eat it, but forcing myself to eat it might even kill me!"

"It's not that exaggerated... but your analogy is still quite vivid and apt."

An Yi's lips twitched slightly. He glanced at the question and still tried to pass on the knowledge to his good friend.

"But even if you don't try to understand the formula, and just use the formula, this problem is actually not difficult."

See, first, we use the completing the square method to balance the equation given in the problem into the standard form of a ternary Cauchy inequality. Then, with a few variations that even an elementary school student could do, you'll find that it's very ingenious...

"Master, Master, please stop chanting! Quickly stop your supernatural powers!"

Wang Xinze covered his head, looking as if he were being tortured by a tight headband.

"Alas, the Great Way is right before your eyes! I, your teacher, have so kindly and earnestly imparted my teachings to you, yet you are so lazy!"

An Yi stopped speaking with a hint of regret, then said with feigned emotion, "If I regret it later, I'll never have such a good opportunity again!"

"Master, is it possible that everyone's spiritual root aptitude is different, and my highest level is only the third grade of the human level? If I continue to cultivate forcibly, I will explode and die?" Wang Xinze showed an expression of "finally alive".

"Hmm, what you said makes some sense."

After careful consideration, An Yi expressed strong agreement with Wang Xinze's point of view, remarking with emotion, "The differences between people can sometimes be quite significant!"

"How so, is there a story behind it?"

Wang Xinze immediately perked up. From An Yi's tone, he could tell that An Yi wasn't just setting the stage to show off, but was genuinely expressing his feelings.

As long as An Yi isn't just showing off but is genuinely "getting beaten up," his good brother will definitely be happy to support him!

"You know these questions were given to me by my older brother, right?" An Yi pointed to a small stack of draft paper filled with questions and answers.

"You know? Oh, I see. You mean you still need to study, while your older brother has already reached the point where he can give you any questions you want, so there's a big gap?"

"No, no, no, if it were just that simple, I wouldn't be so emotional."

An Yi shook his head and briefly explained that there would be a grade-level math exam that afternoon, which would be used to allocate the three direct qualification spots for the National High School Mathematics League. Anyway, this matter was going to be made public; otherwise, there would be no need to hold an exam for the entire grade.

"You know, before he gave me the questions, my older brother said, 'The difficulty will definitely not exceed the first attempt, there won't be any content beyond the syllabus, at most it will just be a little more ingenious and in-depth in terms of method'..."

"etc."

Upon hearing this, Wang Xinze finally realized what was wrong. He widened his eyes and pointed to the ternary Cauchy inequality that An Yi had just written on the draft paper.

"You're telling me this formula isn't beyond the syllabus? How is it not beyond the syllabus? Don't scare me, I have a heart condition! I've absolutely never seen this formula before, and the teacher definitely didn't teach it!"

"After I started working on the problems, I had the same question as you, so after the second class, I went to ask my older brother, and do you know how he explained it?"

An Yi sighed, "She paused for a moment, then thought about it carefully and said that's right, this is the content in the mathematics college entrance examination syllabus, but it's an elective part and won't be tested in the normal college entrance examination. She forgot to distinguish it!"

The most terrifying part of this is that at least I can clearly sense that this is not as difficult as the cultivation techniques we usually learn, so I categorize it into Human Rank 3 and Rank 2. But for my elder brother, she can't even distinguish that; to her, all Rank cultivation techniques are probably equally simple!

"Big brother is indeed worthy of being called the eldest brother... Amazing!" Wang Xinze said with deep respect.

"Big brother is indeed amazing, but I'm in deep trouble! I promised you I'd get good grades in the exam this afternoon, but now I have to learn a whole bunch of second-grade human-level cultivation techniques in a short time!"

"Is...is there enough time?" Wang Xinze was stunned. This seemed impossible to accomplish no matter how you looked at it.

"Heh, it's not that difficult."

An Yi chuckled, "Otherwise, how could I possibly have the time or inclination to chat with you?"

"Get lost!"

Wang Xinze trembled as he raised his middle finger, knowing that despite all his precautions, he had ultimately fallen victim to a scheme.

That bastard got away with it again, damn it!