"Shut up too! Idiot Takei."

Yamaguchi, Takei, and Yoshiko left noisily.

Kato Yusuke looked at a few people, slightly absent-minded.

Suddenly, a hand gently reached towards the top of his head.

"Ah, your hair is a bit messy, let me help you straighten it." Hui said in a calm tone, gently straightening the hair that was messed up by Yamaguchi.

The two were very close.

He could clearly smell the faint fragrance wafting from the girl's body, like a combination of cherry blossoms and milk shower gel.

It smells light and pleasant, but not pungent.

The atmosphere in the class returned to the same liveliness as before.

Some barriers seemed to disappear quietly.

The surrounding sounds seemed to suddenly become quieter.

Kato Yusuke looked around, feeling as if he had never left.

A kind of helpless emotion gathered in the chest.

He squinted his eyes slightly and looked out the window, feeling that the sunshine today was particularly dazzling.

The last thing that became clear was the girl's voice, as clear as a gurgling stream.

"Yeah~ I've done your hair."

…

The morning shift will start at 8:30.

Teacher Nakamura entered the classroom on time.

Intentionally or unintentionally, he glanced at the corner, his eyes flicking past the figure with conspicuous silver-white hair, and the emotions in his eyes flashed away.

Then start hosting the class meeting.

"So, although everyone already knows about the sports meeting this Friday, I still wish you good results and enjoy the youth you lose every year."

"As for the reason why I want to mention this matter again...well, you heard me right, I was just telling you, Kato-san."

Nakamura Masaru put his hands on the podium and said in a tone that was half serious and half joking:

"After such a long rest, show off your energy and win first place in one breath. The teacher's award... no, the honor of our class depends on you, right?"

The students suddenly made a fuss.

"Hey! Teacher, what you just wanted to say was the bonus, right?"

"I heard it too!"

"Wow, what an adult-like speech~"

"Did the teacher put too much pressure on Kato-san?"

"..."

Nakamura Masaru was not annoyed by this, deliberately showing a troubled expression, joking with the students using the excuse of "the spur of love", and after observing the situation, he moved on to the next topic.

"…and then another thing."

He coughed and said: "After the sports meeting, there will be regular exams in mid-October. Please arrange your time reasonably. If your grades are too poor, you will still be asked to take tutoring in the future, right?"

The previous laughter and laughter immediately turned into howls.

After briefly explaining things, it was almost time for the first class.

Leaving instructions for Yusuke to go to the office after class, Nakamura Masaru quickly turned around and left.

…

The first class in the morning is Teacher Matsumoto’s math class.

Teaching progress is currently of a graphical nature.

The teacher drew a quadrilateral ABCD on the blackboard, assuming AB=a, BC=b, ∠A=θ.

It is known that this quadrilateral satisfies:

∠A=∠B=∠C,π/3＜θ＜π/2, b＜a＜b/2cosθ.

Answer the following questions:

1. Assume CD=c, please express c using a, b, θ.

2. Without changing the values ​​of a and b, find the minimum value of c when θ changes within the range of π/3 < θ < π/2.

…

After Mr. Matsumoto finished drawing the picture and writing the question, he looked around the classroom and was attracted by the conspicuous short silver hair in the corner.

After looking at it for a while.

Maybe he wanted to check Yusuke's progress during his absence, or maybe he was simply mocked by his hair color.

Teacher Matsumoto called out his name: "Kato, student number 40, come up and answer the question, including the process."

"..."

Kato Yusuke didn't say anything, he stood up and walked to the podium, took the chalk, and started to solve the problem.

First is the first question.

He took the chalk and added a few strokes to the quadrilateral on the blackboard.

Extend BC, AD; BA, CD.

Considering the midpoint P of AB, it can be seen that EAcosθ=AP.

And because EA=EB,

So EA=EB=a/2cosθ,

In the same way, we can get FB=b/2cosθ.

Then use Menelaus' theorem to write a series of formulas and solve the answer.

c=a-2bcosθ+4cos^2θc

c=(a-2bcosθ)/(1-4cos^2θ)

Teacher Matsumoto folded his arms and stood aside, about to speak...

Ta, da, da, da.

Kato Yusuke answered the second question.

Teacher Matsumoto immediately stopped talking and watched him solve the problem silently.

He held a piece of chalk and wrote continuously on the blackboard, exuding a quiet and calm atmosphere.

Let cosθ=t,

Then c=(a-2bt)/(1-4t^2)

dc/dt=【-2b(1-4t^2)+8t(a-2bt)】/(1-4t^2)^2

If the denominator is positive, simplify the numerator.

Get:-2(4bt^2-4at+b)

Taking into account the range and increase and decrease of the cosine function,

There is a minimum value when t=[a-√(a^2-b^2)]/2b,

Calculate:

c=[a+√(a^2-b^2)]/2

Kato Yusuke put down the chalk and looked at Mr. Matsumoto aside.

Teacher Matsumoto pursed his lips and studied the problem-solving process on the blackboard, the smooth sound of chalk still echoing in his ears.

It was quiet below the classroom.

The students are either thoughtful, frowning in confusion, thinking hard, or drowsy...

Although there were people doing whatever they wanted, no one made any noise.

After all, the man standing on the podium is an old man known for his sternness.

A few moments.

Matsumoto looked away from the blackboard, turned to look at him, and nodded, "Okay, you can go down."

Facing all kinds of looks, Kato Yusuke turned around and returned to his seat.

"Ahem..."

Teacher Matsumoto coughed, attracted the attention of the students, and started speaking in a low voice.
To be continued...