This is the ninth lecture of this course on
Linear Algebra. Here we give a gentle introduction to three dimensional
space, starting with the analog of a grid plane built from a packing of
parallelopipeds in space.
We discuss two different ways of drawing 3D objects in 2D, emphasizing
the importance of parallel projection. Some discussion of the nature of
space and modern physics, then an introduction of affine space via
coordinates. The distinctions between points and vectors is important,
and we talk also about lines and planes.