Fetter and Walecka is a staple of graduate-level physics precisely because it doesn't provide easy answers. The book bridge the gap between undergraduate intuition and the formalisms of Lagrangian Hamiltonian mechanics
While using a manual to get un-stuck is a great way to learn, Fetter and Walecka’s problems are designed to build "mathematical stamina." Relying too heavily on a downloaded ZIP file can rob you of the deep intuition required for qualifying exams. Use these tools to verify your work, not to bypass the struggle of the derivation. Fetter and Walecka is a staple of graduate-level