A Course in Mathematical Analysis Volume 3: Variation of Solutions; Partial Differential Equations of the Second Order; Integral Equations; Calculus of Variations
Classic three-volume study. Volume 1 covers applications to geometry, expansion in series, definite integrals, and derivatives and differentials. Volume 2 explores functions of a complex variable and differential equations. Volume 3 surveys variations of solutions and partial differential equations of the second order and integral equations and calculus of variations.
Here's a sample of other books in this Dover category
A Course in Advanced Calculus by Robert S. Borden An excellent undergraduate text examines sets and structures, limit and continuity in En, measure and integration, differentiable mappings, sequences and series, applications of improper integrals, more. Problems with tips and solutions for some.
Advanced Calculus: Second Edition by David V. Widder Classic text offers exceptionally precise coverage of partial differentiation, vectors, differential geometry, Stieltjes integral, infinite series, gamma function, Fourier series, Laplace transform, much more. Includes exercises and selected answers.
Advanced Calculus of Several Variables by C. H. Edwards, Jr. Modern conceptual treatment of multivariable calculus, emphasizing interplay of geometry and analysis via linear algebra and the approximation of nonlinear mappings by linear ones. Over 400 well-chosen problems. 1973 edition.