I am a college physics grad. For many subtopics of precalculus or calculus, the following statement applies to me: "I can easily solve problems that involve X, but I can't really tell you what X is or why it matters." I'd like to spend some spare time to gain a strong understanding of the central concepts of precalculus or calculus that I only learned superficially. Can anyone recommend a text to work from, based on the following criteria? - Covers precalculus or Calculus BC material. - Focused only on the fundamentals and central concepts. For example, I want to understand integration by substitution, but I don't need or want to review every substitution technique. - NOT focused on (1) tricks, (2) rote problem solving, or (3) teaching general problem solving techniques - Ideal for self study Thanks!