By establishing the coordinate system and solving the plane equation, we can easily solve the problems of finding the intersection of two surfaces or the intersection of a straight line and a surface.

Two other tips are provided:

1.Ax+By+Cy= constant. The vertical vector of this surface is (a, b, c). I often use this, and I can study the proof process by myself.

2. A three-dimensional shape with n vertices, the coordinates of the center of gravity are:

Mx= (sum of x coordinates of all points) /n

My= (sum of Y coordinates of all points) /n

Mz= (sum of z coordinates of all points) /n