Projection formula of a straight line on another straight line

Projection is a concept in mathematics and physics, which exists in many concepts such as set theory, linear algebra, geometry, topology and so on. In plane geometry, a figure similar to a figure is called the projection of this figure.

The projective theorem applies to right triangles. The so-called projection is the orthographic projection. Among them, the vertical foot from a point to a straight line is called the orthogonal projection of the point on this straight line. The line segment between the orthographic projections of two endpoints of a line segment on a straight line is called the orthographic projection of the line segment on the straight line.