Section 3.2

I've never heard of a pseudoinverse before but it seems pretty simple to understand and has useful properties. Orthogonality and orthonormals are also pretty easy to understand and sound familiar but I can't remember exactly where I've heard of them before. I thought the 2-norm property that applied for the orthogonal vectors was interesting. I thought Theorem 3.2 was interesting and would have been interested in seeing the proof in that. The most difficult part to understand to me was the proof for theorem 3.1.