Shadows on the projection planes

Find the shadow of point P(13, 10, 10) on the vertical plane. The light is an own focus.

Step-by-step solution

Join the focus to the point and extend it to the projection plane.
If the light is improper, draw through the point a parallel to the light direction.
Where that line cuts the plane is the shadow.
If the plane is on the light side, there is no shadow: the point does not cast one.

Result: S(33, 0, -40).

The shadow of a point is the trace of the light-point line with the plane; if that trace falls behind the focus, it does not exist.