Note when drawing a circle:

The needle tip must be fixed at one point and cannot move; The distance between the two feet must remain the same; Turn one round end to end.

2. Center symmetry: On a plane, a figure rotates around a certain point 180. If the rotated figures are completely coincident, then this figure is called a central symmetric figure, and this point is called its symmetric center.

Painting method:

(1) Draw two diagonal lines of a square;

(2) Draw a circle with the diagonal intersection as the center and the side length as the diameter.

Pi is the ratio of circumference to diameter. After numerous experiments, it is found that the ratio of circumference to diameter is always a fixed number, which is about 3. 14 159 16, and usually the value is 3. 14. Because this pi was first discovered in Zu Chongzhi, China, it is sometimes called ancestor ratio.