A Modern Course on Curves and Surfaces, 2003, by Richard S Palais
This is a introduction to differential geometry. Prerequisites are: multi-variable calculus, linear algebra, ordinary differential equations.
It is from professor Richard S Palais [http://vmm.math.uci.edu], Virtual Math Museum at http://virtualmathmuseum.org/Surface/gallery_o.html
If you have a question, put $5 at patreon and message me.