Numerical Optimization, Jorge Nocedal and Stephen J. Wright, 2006 (Springer)DOI: 10.1007/978-0-387-40065-5 - A foundational textbook providing a comprehensive theoretical and practical treatment of Quasi-Newton methods, including the secant condition and BFGS.
Convex Optimization, Stephen Boyd and Lieven Vandenberghe, 2004 (Cambridge University Press) - A widely respected textbook that covers foundational optimization algorithms, offering a clear discussion of Quasi-Newton methods within the context of convex optimization.