Elementary Linear Algebra: Applications Version, 11th Edition (http://bcs.wiley.com/he-bcs/Books?action=index&itemId=1118434412&bcsId=8466)

Real coordinate spaces(https://www.khanacademy.org/math/linear-algebra/vectors-and-spaces/vectors/v/real-coordinate-spaces)

Introduction to the null space of a matrix (https://www.khanacademy.org/math/linear-algebra/vectors-and-spaces/null-column-space/v/introduction-to-the-null-space-of-a-matrix)

Visualizing a column space as a plane in R3 (https://www.khanacademy.org/math/linear-algebra/vectors-and-spaces/null-column-space/v/visualizing-a-column-space-as-a-plane-in-r3)