The Angle Between Complementary Subspaces
Ilse C. F. Ipsen, Carl Dean Meyer · American Mathematical Monthly · 1995
Although the concept of angles between general subspaces may be too advanced for an under-graduate linear algebra course, the angle between complementary subspaces can be readily under-stood from basic properties of projectors and matrix norms. The purpose of this article is to derive some simple formulas for the angle between a pair of complementary subspaces by employing only elementary techniques.