1. The man is described by the vector (Drawn in black).
2. The direction of the sunlight is described by .
3. The ray of sunlight which passes over the head of the man is described by the equation of the line l:
x,y,z)=(0,0,2)+t \cdot (-1,0,-1)" alt="lx,y,z)=(0,0,2)+t \cdot (-1,0,-1)" />
4. The equation of the plane p can be written as:
5. Now calculate
6. The point where the ray hits the plane - that means the point where the shadow of the man ends - is . So the length of the shadow is (Drawn in red)