1. Vector cross product: For two non-zero vectors A and B, the vector C obtained by cross product a×b is perpendicular to the plane where A and B are located, and satisfies | c | = | a ||| b | sin θ, where θ is the included angle between A and B 1.

2. Unit normal vector of plane vector: for a non-zero vector A, its unit normal vector n =1| A | (Y component of A, X component of -a) 2.

3. Unit normal vector of space vector: For two non-zero vectors A and B, the vector C obtained by their cross product a×b is the normal vector of their plane, and then the unit normal vector 2 can be obtained by dividing c by |c|.

4. Using the theorem of vector * * * line: For points A, B and C with three non * * lines, the normal vector n of their plane can be expressed as n=k(AB×AC), where k is an arbitrary constant.