Middle school mathematics, mainly learning the projection of points, lines and surfaces;

Projection of a point: from a point perpendicular to a straight line or a plane, the vertical foot is the projection of the point;

Projection of a straight line: the projective connection of points on a straight line segment is the projection of this straight line segment;

Projection of a surface: the total projection of all points on a surface is the projection of this surface;

Therefore, there is no difference between positive and negative projection, so you can refer to the "projection theorem" related to this concept.

2. About projection:

In middle school mathematics, projection is mainly related to vector projection, which can be any real number, positive and negative (version A is compulsory for four students in high school mathematics);

Related to projection is the concept of "orthographic projection", which refers to projection.

According to the definition in People's Education Edition B, the projection of a vector is a vector (that is, the shadow vector pointing to the same side), and the vector projection is the number of vector projections;

3. Summary: For an object without direction, projection or projection is not positive or negative; If there is a directional body, its projection or projection will be positive or negative or directional.