You don't need a whole course in formal logic. The only things that will be really useful to you in the LR section are negating the assumption, and contrapositives. You need not read an entire book or take a course on formal logic to master those basic concepts.
If you are genuinely interested in formal logic, and have the time, sure, go ahead and read the book or take the class. But, why would you waste your time reading/studying a great deal of information that is neither interesting or useful?