"If we want to learn graph theory, we must know what it is," said Teacher Ning.
Yes! All the students nodded together.
"Now, we know its definition based on the student's answer. But we must be curious why we should use the map as the research object to establish such a discipline. There are reasons for everything, right? Just like we humans always want to know why about the origin of everything, including the origin of the earth. This helps to understand the essence of things."
All the students nodded after listening to Teacher Ning's words, as if they were saying, "Teacher, please speak quickly, we can't stand it anymore."
"The origin of graph theory was in 1738. Swedish mathematician Euler." Ning Yunxi wrote a string of English Leornhard Euler on the blackboard, and pointed it in chalk, saying, "This great mathematician solved the Konesburg problem. Graph theory was born. So Euler was the founder of graph theory."
Everyone who listens to the lecture understands the meaning of Teacher Ning’s name writing a mathematician. Great scientists need to be remembered in their hearts for the rest of their lives. We must respect knowledge, and we must respect our ancestors who created knowledge.
"What is the Konesburg problem?" Teacher Ning continued, "Its exact name is the Konesburg Seven Bridges problem, which is the first graph theory problem in the world. However, it comes from a real thing in real life. It can be said that it proves that our mathematics comes from life rather than completely abstract. Based on this, we can see how mathematics is applied specifically to practice. At that time, Konesburg, East Prussia, is the urban area of ​​Kaliningrad, Russia today, crosses the banks of the Pregolia River. There are two small islands in the center of the river. There are seven bridges connected to the two banks of the river. How can we walk all the bridges in this place when we can only walk once?"
The students picked up paper and pen and drew it on their exercise books according to Teacher Ning's description.
The two sides of the straits and the two islands are abstracted from four points. The seven bridges can be regarded as seven connections between the four points.
Ning Yunxi looked at the drawings of the students below, nodded and affirmed, and asked, "How is it, is it difficult?"
The picture was drawn, but how to connect the figures with the problem, all the students suddenly became a little enlightened: Isn’t this the topic that Teacher Ning said at the beginning, using the picture as the research object?
It turns out that this is how graph theory comes about.
"I feel that there are many methods. I don't know which method works." The students below answered Teacher Ning.
"I'll ask you first, how many ways do you think there will be?"
The students looked at each other: I don’t know!
I can't count it.
The teachers in the classroom nodded one by one: No student in the classroom felt bored, which is the benchmark for a good teacher.
“5040 kinds.”
After Teacher Ning threw out such an amazing number, there was a lot of boasts in the classroom. These soldiers who were so serene and serious about the class had very active and vivid expressions at this time. Some students took the initiative to reach out and asked to speak: "Teacher Ning, since there are so many ways to walk, which way to walk can be done?"
In response, Teacher Ning shook his head: "No."
All the students asked again: There was no one?
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Chapter completed!