I know this is not the right place for this post but I cannot post in the science education subforum so I post my question here. I need a good resource - textbook, online resource, video lecture etc.- that explains the multivariate calculus really well; the topics I want to make clear are the Hessian Matrix concept and the classification of extrema for functions of several variables, partial derivatives and identities related with them together with their proofs, some nice discussion on reciprocals of (partial) derivatives, and change of variables for multidimensional integrals and the Jacobian Matrix. These are the topics that I was able to recall at the moment. I would appreciate it if you could guide me on these matter. Thanks in advance