From above, you can see five; Remove the repeated parts from the front and you can see 1. This is not a difficult problem. When I do this kind of problem, I first think about which side is most likely to give me a three-dimensional sense, and then take this as a benchmark and put it in my mind to imagine looking at it from the front.

Drawing is to draw its three-dimensional view (front view, side view, top view,) and corresponding numbers on the corresponding visual icons (because it has no side view, there are three drawing methods, see figure).

plane geometry

Can be divided into the following categories:

(1) circle: including perfect circle, ellipse and multifocal circle-ellipse.

(2) Polygons: triangles, quadrangles, pentagons, etc.

(3) Bows: excellent bows, poor bows, parabolic bows, etc.

(4) Arc: crescent moon, pattern, Tai Chi, gourd, etc.