Introduction to Linear Algebra, Gilbert Strang, 2016 (Wellesley-Cambridge Press) - A standard textbook for linear algebra, covering vector properties, magnitude, and direction.
Deep Learning, Ian Goodfellow, Yoshua Bengio, and Aaron Courville, 2016 (MIT Press)DOI: 10.7551/mitpress/9780262035613.001.0001 - Chapter 2 provides a mathematical background, including a discussion of vectors, norms, and their application in machine learning.
Linear Algebra (18.06SC), Gilbert Strang, 2011 (MIT OpenCourseWare) - A video lecture series offering an accessible introduction to linear algebra, including vectors, magnitude, and unit vectors.