In math class, the math teacher led us to the playground to form a big square with a side length of 100 meters. The teacher asked two students to straighten the 50-meter-long rope, and then organized us to stand outside the long rope, about 10 meters away from one student. The students were very active, and finally they formed a big square that was not very standard. The bell rang. This class let me know that the area of the school playground is about 1 hectare. This course is really interesting!