(20 12- 12- 18 2 1:4 1:2 1)

Label:

mathematics

life

observe

campus

Classification: Kingdom of Mathematics

At the beginning of class, we sat squarely in our seats, only to see Miss Li enter the classroom with boxes, balls and several large and small cylinders. "The teacher brings so many objects, this class must be very interesting!" I took the bait.

Miss Li put a small desk and chair on the platform, on which a big cuboid was placed. The cuboid is facing me, and the words "small medicine box" are written on it. She asked the whole class to observe the "small medicine box" carefully first, and then reported the observation results to her. I sat in the fourth row of the second group and clearly saw the words "small medicine box" in front. But when reporting, several students in the first group actually said they saw three faces. Many of us don't believe it. I was so anxious that I stood up and raised my hand to question. Teacher Li gave me the opportunity to stand in the middle of the first group and observe the cuboid again. Gee, I also saw three faces. Teacher Li didn't let me go back to my seat, but let me stand in the first row of the second group to observe. This time, I saw not only the "small medicine cabinet", but also the red "+"on it. The students strongly demanded to exchange seats again, and Teacher Li readily agreed that the learning atmosphere in the classroom was relaxed and pleasant. Finally, we find that when we look at the same object from different directions, the observed situation is often different. We can see one side and two sides of an object, and we can only see three sides at most. We also found that no matter where we are, it is impossible to see two opposite faces of a cuboid at the same time.

Mr. Li picked up the chalk, turned around and wrote the words "viewing things" on the blackboard, then suddenly recited a poem named Xilin Wall by Su Shi, a poet in the Song Dynasty. The students are very strange. How did the math class suddenly become a Chinese class? Just as we looked at each other, the bell rang. Teacher Li smiled mysteriously and left us a question: "Please think after class: What are the similarities between Su Shi's visit to Lushan and our observation of objects?"

I learned this poem in the fourth grade Chinese class, but what does it have to do with observing objects in today's math class? As soon as Mr. Li left the classroom, we got together and chattered, without going to the toilet or drinking water. "Think of the mountain side as a mountain peak, and the distance is different. I don't know the true face of Lushan Mountain, but toward which corner of the mountain. " This famous saying once made many people daydream about the wonders of Lushan Mountain. We recited it repeatedly together, and finally realized that the Lushan Mountain written by the poet can present different forms, because the poet appreciates Lushan Mountain from different angles. Then when we observe an object, just like enjoying the scenery of Lushan Mountain, there is a problem of choosing a flexible observation angle. If the observation angle is chosen properly, it will bring us a lot of convenience in analyzing problems. Therefore, in the future study, we should observe things from multiple angles and think more. ...

(Instructor: Li Lin)

The unit "observing objects" is really interesting. I didn't expect to find so much mathematical knowledge in the process of observation. Observing an object, one can't observe everything, so one should cooperate with one's study partners. When observing, we should pay attention to identify the main characteristics of the object, think about the difference between observing the same object in different positions while observing, and then communicate with our classmates.

I found that a rectangle has two symmetry axes, a square has four symmetry axes, and a circle has countless symmetry axes. Mirror symmetry is more interesting. For example, the clock face in the mirror is 9:00 3:00, and 1: 00 is 1 1: 00, which is opposite to the real thing.