Self-Contradiction (1)
“The six trigonometric differentiation formulas—you need to memorize all of them.”
Scratch, scratch.
The sound of writing on the board spread through the classroom.
“Secant and tangent are friends, and cosecant and cotangent are friends. If you think of it this way, it’s easy to memorize. When you differentiate tangent x, it becomes secant squared x, and when you differentiate cotangent x, it becomes minus cosecant squared x.”
Seo Juhan swiftly wrote out the formulas with white chalk. On the green chalkboard remained white marks from the previous class period, like stains.
“Also, some have minus signs and some don’t… If it starts with ‘co’ like cosine, cosecant, cotangent, then it has a minus sign. If you memorize it this way, you won’t get confused.”
After finishing his explanation, Seo Juhan solved a simple example problem and turned around.
“Now, try solving problems 3 and 4 on page 61 yourself.”
Seo Juhan said while looking at the college entrance exam prep book spread out on the teacher’s desk.
Only the sound of pages turning echoed in the classroom. That quietness made Seo Juhan even more nervous for no reason.
The class he was in charge of had better classroom behavior compared to other classes, but honestly, it wasn’t usually this good.
Of course, that was only relative—he couldn’t say they were studious. They also fell far short of having a wholesome and diligent attitude.
Even so, today was strange enough. It was suspiciously quiet.
Considering that adults who looked closer to gangsters in their appearance were sitting there in shabby attire, it was even more abnormal.
Seo Juhan tried hard not to consciously look at the back seats and just looked down at his book.
Filling 50 minutes with only basic-level content was actually harder. He tried to kill time by solving problems, but the calculations finished in his head. He resented the time that didn’t flow easily.
“Teacher.”
Seo Juhan remained silent, reading problems from the next chapter.
“Teacher!”
Only after hearing a loud voice that broke the silence did he raise his head.
“Uh… huh?”
The one who called him was Kim Gichan sitting in the front row.
He was a guy who sublimated his lacking intelligence and hopeless future with intuition and positivity. It felt like just yesterday that he’d gone to the police box because of that punk, but it already seemed ages ago.
“Over here.”
Seo Juhan rolled his eyes in the direction Kim Gichan was pointing.
Go Un had his hand raised.
Seeing that, Seo Juhan’s facial muscles involuntarily contorted.
“…Why?”
Seo Juhan asked reluctantly while trying hard to suppress a rotting smile.
“I don’t really understand this.”
It was an unbearably ordinary voice.
At Yangseong School, it was a model student-like question he’d never heard except from that guy. Someone who didn’t know better might think he was a good student.
“Ah… really?”
Seo Juhan answered indifferently but couldn’t easily move his feet. If it had been last week, he would have helped wholeheartedly while feeling self-efficacy, but the situation had changed too much.
An uncomfortable silence continued as if even breathing had stopped. The heavy air pressed down on his shoulders like a thousand pounds.
How could he make a tactful refusal?
Separate from his desperate feelings, no solution came to mind for overcoming this crisis.
Seo Juhan had the obligation to endure the set time in this classroom whether it killed him or not. And he was a chicken who had never committed the act of betraying his responsibilities in life.
He had no choice but to move his feet. He tried to drag out the time with the slowest movements possible, but even so, the distance from one end of the classroom to the other wasn’t much.
“…What don’t you understand?”
“This.”
Go Un tapped the problem with the back of his mechanical pencil.
The guy was sitting with his legs spread so wide that the desk looked cramped. That posture looked incredibly arrogant.
Seo Juhan stopped at a place where he could gauge what the problem was while maintaining maximum distance from Go Un. Then he quickly skimmed the problem with his eyes.
Recalling Go Un’s abilities that he’d observed until now, it wasn’t to the point where he couldn’t solve it himself.
Of course, that didn’t mean Go Un was excellent. It just meant he was somewhat better than the other blockheads whose IQ numbers he doubted reached three digits.
Was he really asking because he didn’t know?
Although reasonable doubt arose, he couldn’t very well ask that when there were so many watching eyes.
“Here, the difference between pi plus h and pi minus h is 2h, right? So it’s the same as twice f prime pi.”
Seo Juhan explained appropriately with his arms crossed as if putting up a defensive barrier.
“So if you find what f prime theta is… When you differentiate tangent, it becomes secant squared x, but since it’s a composite function, you need to add 2 in front, and when you differentiate sine x, it becomes cosine. Then if you substitute pi for the x value…”
Seo Juhan continued speaking in a blunt voice while only looking at the book.
“Since secant is the reciprocal of cosine, the front is 2, and the back is minus 3. When you calculate it, it’s minus 2.”
After hurriedly finishing the explanation, he quickly moved his feet.
“Wait a moment.”
A heavy voice grabbed his ankle.
“I still don’t really understand.”
Seo Juhan looked down disapprovingly at the jet-black crown of his head. There was a neatly formed cowlick. The pitch-black stray hairs gently swayed in the wind coming from outside the window. The way it exuded peacefulness was extremely irritating.
“It’s not a difficult problem. Just apply what you memorized, okay?”
A prickly voice came out naturally.
“Just listening to words, I don’t really understand.”
The back of the mechanical pencil held in his left hand tapped the smooth paper.
“…Why don’t you understand that? It’s almost exactly the same as what I solved earlier.”
“I know, right. Is it because I’m a blockhead?”
What came back was a voice quietly tinged with laughter.
“…”
Seo Juhan was at a loss for words.
So he did hear it.
It was the day he’d encountered Go Un while walking to the annex building in the spring breeze. It seemed he’d heard everything when Seo Juhan had been on the phone with Lee Donghyuk describing Yangseong School students as ‘blockheads.’ It was somewhat absurd that he’d been holding onto that and was bringing it out now.
“Please explain it one more time.”
Go Un raised his head as he finished speaking. Suddenly, his black pupils curved like crescent moons.
“…”
Seo Juhan’s breath caught. His chest felt stuffy as if his throat was choked.
The brief eye contact stretched out long like slow motion. As if bound by shackles, he couldn’t easily avert his gaze. They were black hole-like eyes where it wasn’t easy to distinguish between iris and pupil. It felt like being sucked into a deep abyss.
Thud!
From somewhere came the noise of a book falling to the floor. Go Un’s black eyes glanced behind Seo Juhan with a displeased expression.
Only then did Seo Juhan barely regain his senses.
“…Try solving it once the way I told you. I’ll check it.”
“I don’t know how to solve it though.”
“…Then write what I say. 2 f prime x is 2 secant squared 2x plus 3 cosine x.”
Seo Juhan recited the solution in a monotone voice, but the hand holding the mechanical pencil didn’t move at all.
“What are you doing? I said write it.”
“I don’t want to solve it mechanically.”
Go Un jutted out his lips.
“The teacher didn’t tell me. Why tangent becomes secant squared x when you differentiate it.”
“…Just memorize it.”
“You have to tell me why it becomes that for me to memorize it.”
Go Un raised one eyebrow.
As if you could understand it anyway.
“It’s better to just memorize it. Are you going to derive each process step by step to solve problems in the exam room too?”
“I can’t memorize it if I don’t understand it though.”
Seo Juhan gradually became more annoyed at the stagnant development that wasn’t going his way.
“Are you going to do that during exams too? Hold onto it until it’s solved?”
“But it’s not exam time right now.”
The attitude of not losing even one word scratched at Seo Juhan’s sense of authority. His jaw muscles naturally tensed up.
“I’ll tell you for now, so write it down.”
Seo Juhan said while pretending to be detached.
“Teacher, you solve it once.”
Go Un lightly supported his chin with his other hand and wiggled the tip of his mechanical pencil.
“You have to solve it to understand it.”
“How can I solve it when I don’t understand it?”
Their gazes clashed sharply. It was somewhere between the eye level of the standing Seo Juhan and Go Un sitting in the chair.
The air tightened like a thread pulled taut just before breaking.
The atmosphere of the classroom, where traces of time could be felt, sank heavily.
