This flag is one after the other.

I have to say that all the people present are ruthless, and it seems that they are going to be on the same page as Lin Bei today.

Not only the people who were jealous of Lin Bei before, but also many people watching the fire from the other side of the river participated.

Neither hatred nor resentment.

And it's purely to watch the excitement and not think it's a big deal.

Of course.

The happiest people have to belong to Yang Juntian and others, constantly stirring up waves and fanning the flames next to them.

Don't ask why.

Ask.

It's just that Lin Bei has answered two questions in a row just now, causing them to be slapped in the face one after another, and they are completely mad.

Especially Yang Juntian.

How he wanted to see Lin Bei frustrated once!

So he set up the most flags and the most ruthless, and any handstand shampoo was weak, and he directly turned upside down.

It's not that he wants to cheat and cheat, but this time he has enough confidence, Lin Bei will definitely not be able to do this.

After all.

This question is really difficult.

He didn't have a single idea himself, so he didn't have a single idea.

He also quietly asked Lu Ren, the representative of the mathematics class next to him, and Chu Bufan, the class leader, two top students.

The result is......

Whether it was Lu Ren or Chu Bufan, they all shook their heads for a while, secretly sighing that this question was not easy to solve.

Although the stem is simple.

But if you really want to calculate, it is not generally complicated, and it takes a lot of time to deduce slowly.

Maybe the entire class, only Zeng Xi, the school committee, can handle it, and others estimate that it is impossible.

As for Lin Bei, it is even more unlikely.

Even if Lin Bei has already met a dead mouse and touched two questions correctly, this third question will definitely not be.

Unless Lin Bei's mathematical strength can surpass him, Lu Ren and Chu Bufan and others, and catch up with Zeng Xi's height.

Gee!

Zeng Xi is the first student in the class!

In the whole school, it is famous, and the grade ranking is stable in the top 20, and even in the top 10.

Among the girls, the strength is second only to the school flower goddess Zhao Qinghan, and the bullfrogs can be described as a group, which can be called the pride of the sky.

Although Lin Bei is now closer to Zeng Xi.

But getting closer, doesn't mean that Lin Bei's strength is as strong as Zeng Xi!

But the next second.

Yang Juntian was about to vomit blood again.

Saw......

After the math teacher Yu Huatian finished writing the question, he smiled meaningfully and handed over the chalk, "Come, Lin Bei, the chalk is for you, come up and solve it!" ”

"This question is a solution question, which is slightly more difficult than the two questions just now, and it is estimated that it is not easy to make it."

"...... like this"

"I'll give you fifteen minutes, and you can play freely to explain and see how much you can write."

"Don't be too pushy, after all, you've already made two questions and proven your strength."

"This time the test paper is full of marks, the teacher believes that you did it yourself, and I apologize to you for the previous distrust."

I have to say.

Mathematics teacher Yu Huatian can still deal with it, and after understanding his mistake, he actually apologized to Lin Bei in public.

That attitude is also a good batch.

But an apology is an apology.

This face is also to earn back a little.

Although he said that the above question was only slightly difficult, he knew from the tone that he was being humble.

As a matter of fact.

He thinks that Lin Bei will definitely not be able to do this problem.

After all, it is also a derivative finale question, but this difficulty is also divided into three, six, nine and so on.

If the difficulty of the derivative finale of the previous test paper is divided into two or three grades, then this one is five or six grades.

This difficulty has more than doubled.

That's why.

He only gave Lin Bei fifteen minutes not to speak, and asked him not to be too demanding, how much he could write.

However......

Hear him.

Lin Bei didn't take the chalk tip handed over, but only thought for a moment, then waved his hand and shook his head, "Teacher, this question is indeed a bit difficult, but it's okay." ”

"I don't need chalk, I'll just dictate it! This saves a lot of time. ”

Gee!

Lin Bei was really speechless, and he was endless.

Obviously, Yu Huatian gave him chalk and let him think about it slowly, but he didn't use chalk.

Even.

He also wants to save time?

But there's more to come.

I saw that Lin Bei's words had just fallen, and he immediately spoke, "Well, there seem to be two solutions to this problem." ”

"One of them is to use the knowledge of parametric parameters + isomorphism + exponential tangent deflation + hidden zero point to solve."

The stem is x(e^x-a)-2l

x+2l

2-2≥0, it's clear that this is true at x>0. ”

"First, take the open parameter, and it becomes xe^x-2l

x+2l

2-2≥ax，x＞0。 ”

"Then a≤(xe^x-2l

x+2l

2-2)/x，x＞0。 ”

"Let g(x)=(xe^x-2l

x+2l

2-2)/x，x＞0。 ”

"One more isomorphism."

Then g(x)=(e^(x+l

x)-2l

x+2l

2-2)/x。 ”

Then divide the denominator on the right by a 2 to get g(x)=(e^(x+l

x-l

2)-l

x+l

2-1)/(x/2)=(e^(x+l

x-l

2)-(x+l

x-l

2)-1+x)/(x/2)。 ”

"Scale ...... according to linearity"

"f(x)=e^x-x-1≥0, the function is constant, and the equals sign is taken if and only if x=0."

"So ......"

“g(x)=(f(x+l

x-l

2)+x)/(x/2)≥(0+x)/(x/2)=2。 ”

"Then verify the conditions for taking."

Let h(x)=x+l

x-l

2，x＞0。 ”

"h'(x)=1+1/x>0, for x>0 is constant, i.e., h(x) is monotonically increasing at (1, +∞)."

And h(1) = 1-l

2＞0。 ”

“h(1/2)=1/2-2l

2＜0。 ”

"According to the zero-point existence theorem, there must be a unique x0 in the middle of which belongs to (1/2,1) such that h(x0)=0."

"That is, x0+l

x0-l

2=0。 ”

"So when x=x0, take etc."

"So g(x)mi

=g(x0)=2。 ”

"So A≤2."

"Therefore, the range of values of a is (-∞,2]."

Well!

That's the end of the first approach.

It seems to be both complex and simple, as long as the knowledge of parameters, isomorphism, tangent deflation and hidden zero points is integrated, then it only needs to be solved step by step.

But......

Many people present, including Yang Juntian, stared at them directly, with a bewildered expression: "??? ”

Do you have a lot of question marks, children? 】

It couldn't be more accurate to use this sentence to describe the expressions of Yang Juntian and others at this moment.

It's really ......

I was shocked by Lin Bei!

Such a difficult derivative problem, but Lin Bei didn't even use chalk, but directly dictated and solved it?

All of a sudden, the class was quiet.

Everyone looked at Yu Huatian, the math teacher on the podium, wondering if Lin Bei had the right solution.

But Yu Huatian hadn't spoken yet.

Lin Bei continued: "This second method is to use isomorphism + exponential tangent deflation + hidden zero point. ”

"If you don't use parameters, it's a little more complicated."

"That's ......"

"xe^x-ax-2l

x+2l

2-2≥0。 ”

“e^(x+l

x)-2l

x+2l

2-2-ax≥0。 ”

“e^(x+l

x-l

2)-(x+l

x-l

2)-1+(1-a/2)x≥0。 ”

"Let g(x)=e^x-x-1......"

“…… (process omitted) ......"

"Therefore, the range of values for a is (-∞,2], which is the same as the conclusion of the first method."