Love lasts a lifetime

He Yu asked the students;"Except when tanθ takes a positive value, we can find out the angle θ corresponding to tanθ in the trigonometric function table.

But why doesn't it work when tanθ takes a negative value?"

……..

No one answered at this time.

Suddenly a student stood up and said:"I guess if tanθ takes a negative value, it means that the angle between the two straight lines does not exist?"

"Students, think about it, does his guess make sense?"

……..

No one answered!

He Yu said,"If the students don't know, should I tell you, or should I let you use your brains to think about it?"

At this time, a classmate stood up and said,"I think so, because the problem of finding two straight lines is When the tangent value of an included angle is negative, does it mean that the included angle does not exist?"

He Yu said happily;"That's very correct.

This means that letting the students use their own brains to come up with it is more effective and easier than what I said. Mastery.

It’s really rare to have both courage and brainpower.

Now let’s study how to calculate.

This calculation formula is a molecular formula, and the molecule is k1-k2.

We knew in elementary school that the molecule can be zero. If the molecule is When the numerator is zero, what does it mean?

That student will answer it."

A female classmate stood up and said;"If the numerator is zero, it means that the slopes of the two straight lines are equal. There are only two possibilities for the positional relationship between the two straight lines, one is One is parallel, the other is coincidence. Only in these two cases can the slopes be equal.

If anyone wants to refute me, please stand up and say it, and I will humbly ask for advice!"

After she finished speaking, with a very Zhihao look, Scan each classmate once.

He Yu couldn't control it. He clapped his hands happily and said,"I'm really impressed by you!

I thought you didn't use your brain enough in studying, but your performance today really moved me.

When the classmates commented, I said Right?"

A female classmate stood up unceremoniously and said in front of the teacher:"Teacher He!

If it weren't for Li Juan's very beautiful answer, you would never praise her in front of so many people.

You usually are You underestimated our female classmates!

How is Li Juan's performance today?"

Seeing this situation, the leader of the Education Bureau was afraid that He Yu would get angry. Want to persuade. But seeing that He Yu didn't get angry.

Instead, he smiled and said:"Thank you, this classmate, for your criticism of me.

I welcome you to have the courage to criticize me in public.

It's just that I usually look down on you female classmates!

Today I wake up!

You are so diligent Their spirit of studying and studying hard is commendable and I admire them.

I hope that all the students in the class will learn from them!

From now on, I will treat you like male classmates.

Not only will I guide you carefully, but I will also pay attention to you. Tutoring."

Several female classmates clapped their hands happily!

This scene deeply moved the leaders and teachers who came to attend the class!

The leader of the Education Bureau whispered to Principal Yin,"I really admire that your school can establish such a teacher-student relationship!

Why did He Yu get the first place in the college entrance examination?

Today I finally understand the secret."

Principal Yin said,"Say something. To be honest, I started to see these female classmates so disregarding He Yu's face, criticizing and pointing out his usual attitude towards female classmates in front of so many leaders and teachers.

I broke into a cold sweat for He Yu, I don't know why he How to deal with it?

When I heard that instead of losing his temper, he praised them with a smile and enthusiasm, I felt less nervous!"

It's really surprising to accuse the teacher in public. But instead of getting angry, he smiled and said thank you, which was admirable.