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mathwonk said:I do not know what to suggest as the best way to learn proofs. This happens gradually as you practice them. I got my start in high school in a geometry course back when they were proof based, but I still had a lot of trouble with the language. Than as a senior we had a special course out of Principles of mathematics, which began with a chapter on sets and logic. It had a little intro to propositional calculus and truth tables, and I finally found out what a converse was, and a contrapositive, and how to negate things. Basically, in order to prove something you need to know what it would mean for it to be false. And a basic technique is proof by negation, so you need to know that A implies B if and only if notB implies notA. Then I still had trouble in a first year Spivak type proof based calculus course, but it helped more. Then later I had an abstract analysis course, where we proved set theoretic statements about measure theory, and I internalized how to negate lengthy quantified statements.
And if you are getting a C from the good physicist, try for a B. It is often more instructive to get a B from a hard prof than an A from an easy one. (But a D means little from anyone.)
There are some elementary books that claim to teach you how to do proofs but I don't think any of them are much good. One of the best, and maybe hardest, general books to improve your math knowledge is "What is mathematics" by Courant and Robbins. Otherwise it probably helps just to study a proof based book on some specific topic like linear algebra, such as Halmos' Finite dimensional vector spaces.
Thank's I will check out that first book you mentioned during Christmas break.