The grade director began reading the problem aloud:
"If △ABC is an obtuse triangle, find the range of arccos(sin A) + arccos(sin B) + arccos(sin C)."
As the director spoke, the students began to react in all sorts of ways.
Most of them, including the weaker students, listened in a daze. They hadn't even understood what "arc" meant. In high school, arc wasn't a major topic; it was something covered in elementary school. It had only been briefly mentioned in an inconspicuous corner at the bottom of a page in some math textbook. Most students hadn't mastered the material well enough to know what "arc" meant. At best, it sounded vaguely familiar.
Many began whispering among themselves:
"Holy crap, I can't even understand the problem!"
"Math really is a subject that can drive you insane!"
"Chen Zhao must have ten thousand horses galloping through his mind right now..."
"If you can't even understand the problem, how are you supposed to solve it? Might as well dream about it!"
"The director's going to use a hard problem to slap Chen Zhao right in the face! 'You said you could do them all? Here's one you can't do!'"
"Chen Zhao's really lost it today, bragging like that. Now he's stuck with no way out. He could've just stood at the back of the classroom for the morning and been done with it, but instead he's made such a fuss that he'll be going home for a week with a disciplinary warning."
"If Chen Zhao can solve that, I'll eat my test paper right here!"
While the weaker students whispered to one another, several top students in the front row had already picked up their pens and were scribbling on their scratch paper. Chen Miaoran, first in the class; Zhang Shucheng, second; and Liu Chang, third, were all braced for the challenge, trying to solve the problem.
The reason top students were top students was that they went after problems with the same ferocity a wolf showed toward a sheep. They saw a new problem and wanted to solve it; if they couldn't, it bothered them! If a true top student were walking down the street and spotted two things on the ground, a bright red hundred-yuan bill and a page torn from a workbook, their first instinct would absolutely be to pick up the problem, not the money!
Solving problems made me happy! Scores were my life!
But this time, after writing and scribbling on their scratch paper for a few moments, the top students suddenly got stuck. Their faces showed not a trace of happiness, only frustration.
The problem looked simple enough, just one short line asking for a range. But when they actually tried to solve it, they found they had no idea where to start!
It seemed there were too many things to consider, yet it also seemed they might be overthinking it. None of the standard methods worked. They didn't know where to begin if they tried to solve it directly, either. It was like a tiger trying to bite a hedgehog: there was no way in!
Now they had only one last method left: using the answer choices to figure it out. Many multiple-choice questions were difficult to solve directly, but the choices could offer clues. The top students all looked up at the blackboard.
Chen Zhao had already finished writing the problem on the board.
It was a multiple-choice question. The director had just been about to read out the four options when Chen Zhao's hand kept moving. He went to the next line and wrote down the answer directly—
(90°–270°)
After finishing, Chen Zhao turned to the director. "The answer is from ninety to two hundred and seventy degrees, right, sir?"
The whole class erupted!
He'd only just copied down the question, and he already had the answer?!
The students were stunned. How the hell had he been so fast?!
Even if you searched with an app like Xiaoyuan Search or Homework Help, it would take time to snap a photo and upload it. But he'd produced the answer instantly?
The top students in the front row were even more shocked. Outsiders watched the spectacle; insiders understood what was going on. The weaker students couldn't solve a problem like this in the first place, so they had no way of knowing just how difficult it was. They only thought Chen Zhao had calculated the answer quickly. The top students were different. They understood the problem, and that was how they knew how difficult it was to solve!
Liu Chang, third in the class, nudged Zhang Shucheng, second, with his elbow. "Did he get it right?"
Zhang Shucheng stared at him blankly. "I can't solve it!"
Zhang Shucheng poked Chen Miaoran, first in the class, with his pen and quietly asked, "Is Chen Zhao's answer right?"
To his surprise, Chen Miaoran looked just as bewildered. "This problem...I haven't solved it yet. I don't have any ideas for now."
The students nearby overheard the top students talking and were stunned. None of the top three could solve it? Just how hard was this problem?
And Chen Zhao had written down the answer right after copying the question?
What the hell?!
Could he...have just guessed?
The thought occurred to some of the students, and the more they considered it, the more likely it seemed. There was no way Chen Zhao could solve a problem that difficult. Besides, it was a problem from ten years ago, so old it wouldn't even be included in study guides. It was even less likely that Chen Zhao had seen it before and memorized the answer. So there was only one explanation: he'd made a wild guess!
But the director's expression suddenly changed!
"Mm...that's right. That is the answer," the principal said, nodding.
In an instant, the whole class fell silent!
The entire classroom was completely quiet!
He really...had gotten it right?
Every student was bewildered. What was going on? Had the director and Chen Zhao secretly agreed to put on this little act? Impossible! Had someone in the class given Chen Zhao a hint? That couldn't be it, either. None of the top three had solved it! Who could have helped him?
Chen Zhao ignored the class's reaction and looked at the director. "Then please give me the second problem, sir!"
The director nodded, his expression turning complicated. He probably hadn't expected Chen Zhao to work out the problem mentally in one go. Chen Zhao hadn't even needed to do any calculations on the blackboard; he'd just given the answer. It was as if the hardest multiple-choice question on a math exam from ten years ago were as ridiculously easy to him as one plus one equaling two!
After a moment's thought, the director spoke:
"The next problem is the final fill-in-the-blank question from the Hundred Schools Joint Examination held across four provinces five years ago. Listen carefully."
The students' pupils shrank all at once. The Hundred Schools Joint Examination across four provinces!
They had taken that very exam just a month ago. As the name suggested, students from a hundred schools across four provinces had all sat the same test. The exam had been set by award-winning teachers and senior education professors from those four provinces. The problems had been extremely difficult, the question types highly original, and there were a great many of them! In short, it was a devil of an exam!
Just how difficult were the problems on the Hundred Schools Joint Examination across four provinces?
Put it this way: some students could score five hundred on their school's midterms and finals, but scored less than four hundred on the joint examination!
And now the director was going to give Chen Zhao the hardest fill-in-the-blank problem from the exam!
He was trying to kill Chen Zhao!
The director suddenly picked up a piece of chalk and a ruler from the lectern and began drawing on the blackboard himself.
Clearly, this problem involved solving something using a diagram!
Amidst the sharp taps and scrapes of chalk, a bizarre geometric figure appeared, strange enough to make people dizzy! It showed three cylinders, two lying on top of one another, with a plane slicing through all three from the upper left to the lower right, exposing irregular cross-sections!
"Find the functions of this line and this line," the director said, thickening two lines on the diagram.
The whole class was stunned!
A god-tier problem!
Before you continue