[rramadass]

I suggest spending less time with online lectures/videos etc. and more time with actual Books. The online stuff should be an adjunct to your study of books. Also it is best if you look at books dealing with a survey of all the relevant topics required for Science/Engineering before delving into specialized ones. To that end, i can recommend the following;

Mathematical Techniques: An Introduction for the Engineering, Physical, and Mathematical Sciences by Jordan and Smith - This book is really accessible.

Mathematical Methods for Physics and Engineering: A Comprehensive Guide by Riley, Hobson, Bence - A more advanced coverage of topics than the one above.

Mathematics for Physicists: Introductory Concepts and Methods by Altland and Delft - The coverage is excellent but somewhat challenging to read.