If you are stuck on a specific proof (e.g., in Chapter 8 regarding Line Integrals), searching the specific problem statement on Stack Exchange will often lead to a detailed PDF-style explanation. How to Use Solutions Without Hurting Your Progress
For individual problems, post the exact question number (e.g., "Apostol Vol 2, Section 4.12, Problem 9") to Math Stack Exchange. The community is active and often provides complete, rigorous solutions. Over time, you can compile these into your personal PDF. tom apostol calculus vol 2 solutions pdf