Convex Optimization, Stephen Boyd and Lieven Vandenberghe, 2004 (Cambridge University Press) - A classic and comprehensive textbook that provides a rigorous theoretical foundation for Lagrangian duality, KKT conditions, and convex optimization, highly relevant to the course content.
Lagrangian Duality, Stephen Boyd, 2004 (Stanford University) - Excellent lecture notes from Stanford University's EE364A course (Convex Optimization I), offering a clear and concise explanation of Lagrangian duality and KKT conditions.