my scientific age

Chapter 20 You mean, 30 yuan ocean?
“第二个答案由［0，2π）内，cosπ/3=cos5π/3=1/2，结合余弦线就能得出cosα≤1/2的解集，最难的部分其实是第三个，已知［0，2π）内，｜sinπ/4｜=｜cosπ/4｜=｜sin3π/4｜=｜cos3π/4｜=｜sin5π/4｜=｜cos5π/4｜=｜sin7π/4｜=｜sin7π/4｜=√2￣/2，结合余弦线和正弦线，所以｜cosα｜＞｜sinα｜的解集为｛α｜kπ-π/4＜α＜kπ+π/4，k∈Z｝，你看，是不是很简单？”

After the whole paragraph was finished, Yu Hua gasped slightly. After explaining the problem-solving ideas, he finally had the feeling that he used to be a high school math teacher. His throat was too sore to teach a class.

"..."

The thin boy sitting next to him looked at the scratch paper and then at Yu Hua's gasping appearance, his face full of confusion.

Simple?
This thing really can be called, simple? ? ?
Looking at the densely packed scratch paper, the thin boy's mind was full of a series of question marks. He really couldn't get up the courage and regarded this incomprehensible scratch paper as simple.

He couldn't understand the topics written above, and the topics above also sneered at him as a scumbag.

"Uh, did I talk too fast?" Yu Hua came back to his senses, saw the thin boy, scratched his head, a little embarrassed, and felt very guilty: "I talk faster, and many steps are simplified directly. Sorry, sorry."

I'm really sorry, I've never been a scholar in my two lifetimes, so it seems like I shouldn't simplify many necessary detailed steps.

The thin boy came back to his senses, looked at Yu Hua, who was full of guilt, and bowed his head to apologize: "I'm sorry, I'm too stupid."

"No, if not, just practice more on this kind of problem. Come, come, I will continue to teach you. Look at this problem, there are three sub-questions in total, of which the first sub-question and the second sub-question are relatively simple, we only You need to draw a trigonometric function line to find it. The third sub-question is more complicated and involves the feasible region. It is not very good to draw here. There are three ways to draw, and I will teach you the easiest way to draw..." Yu Hua shook his head. There is no idiot who can go to Peiping No. [-] Middle School. The only difference is whether the foundation is firm or not. The words are calm and start from the beginning.

Helping people to the end, isn't it appropriate not to form a classmate relationship?

This is not appropriate.

As a young man who is striving for the goal of being a scholar, helping students with poor grades to progress is the foundation.

Seeing Yu Hua with a serious face, the thin boy was startled for a moment. He quickly concentrated and listened carefully. He held the scratch paper and pen in his right hand, and wrote down the problem-solving method that Yu Hua described.

From the solution of the first sub-question to the solution of the third sub-question, Yu Hua gave the formula and process of each step in detail, and then gave the reason why this formula was used, and the content of each formula of the trigonometric function line. Like the most sincere student, he kept nodding his head to record.

after awhile.

"Student Yu Hua, thank you so much. I didn't understand what the previous Mr. Ren said about this question. After listening to you this time, I finally understand, Niu." The thin classmate who solved the final problem felt that the whole learning world seemed to have opened a new door. He stood up and thanked Yu Huazuo, his face full of gratitude.

He finally solved the final problem of the trigonometric function line solution inequalities that had puzzled him. The key point was that he mastered the solution to this problem.

Although, in Yu Hua's mouth, this is the simplest one.

But that's enough.

"It's okay, I just did what a high school student should do." The harvest came from the praise and gratitude of the thin classmates. Although there was no substantial return, Yu Hua was very happy and smiled.

One word, comfortable.

It turns out that this is what it feels like to be a scholar.

"Student Yu Hua, I have an unkind request. Can you teach me other knowledge points about trigonometry? Trigonometric function lines prove that trigonometric function inequalities, the domain of definition of trigonometric functions, and trigonometric identity transformations are all my weaknesses. "The thin boy's eyes showed a trace of anticipation. Looking at Yu Hua, who was modest and confident, he looked embarrassed: "I..."

At this moment, before the thin classmate could finish speaking, Yu Hua's face stiffened when he heard this tone, the smile on his face disappeared instantly, he quickly stopped, and cracked a refusal word: "Wait... I'm sorry classmate, the studies are heavy, for the time being. I don't have time to teach, and I don't learn much."

Teach other knowledge points?
Yu Hua is not prepared to do such a thankless task. He still has to tackle mathematics, strive for perfect grades, go to see Hua Luogeng, and then study the three lessons of physical and chemical biology.

When it's time to help classmates, help, and when it's time to defend your own interests, you must defend it.

Don't waste time!
When the words fell, just when Yu Hua had already thought of the second way of refusing, he heard the weak and unassuming words of the skinny boy again: "I... I can give you 30 yuan in return. "

After some unfounded words, the thin boy lowered his head.

"I really don't have time..." Yu Hua was about to say the second kind of refusal, when three words came out of his throat, and suddenly found that his throat seemed to be restrained by some invisible force. He was stunned and reacted. , a little confused.

what did i hear?
Marlene on, I seem to hear the call of my dear silver dollar?

"Wait, you mean, 30 yuan?" Yu Hua's eyes widened, looking at the thin boy with his head bowed and feeling inferior, he suspected that he had heard it wrong.

"I'm sorry, Yu Hua, I... I only have so much money for the New Year this year, is that okay?"

Hearing Yu Hua's voice, the skinny boy buried his head even lower, stammered a little, and didn't dare to look up at Yu Hua's expression. He knew that 30 yuan won't solve the problem, and he seemed extremely inferior. He wanted to improve his grades, but he didn't want to pay the price , Where in the world is there such a good thing.

ashamed.

uncomfortable.

The money wasn't enough, he knew.

But he really has no choice. The money he can control independently is only 30 yuan, which is still this year's lucky money.

"Gollum."

Swallowing saliva in his throat, Yu Hua looked at the thin boy with a face full of inferiority in front of him, thinking of the other person's words in his ears, he kept persuading himself to be steady, his right hand trembled slightly, tried to control, and patted the thin boy on the shoulder: "Yes, of course. Helping my classmates to improve and improve their grades is what I should do.”

Between the words, there was even a tremor.

Gan!
What the hell kind of family is this? The New Year's money alone costs 30 yuan! ! !
For the sake of Yin Yuan's face, ah no, for the sake of helping his classmates progress and improving their grades, he did this job of tutoring.

As for time?

As the saying goes: time is money.

"Really?" Hearing Yu Hua's answer, the thin boy immediately raised his head with a look of surprise on his face.

(End of this chapter)