1. The problem statement, all variables and given/known data A couple questions that have been building up here. I usually don't see them explicitly answered in the text. When can you take the limit of both sides of an equation? And can you get rid of the limit from both sides of an equation? How about taking the derivative or integral of both sides? Can you ever take the absolute value of both sides? What about taking the sup or inf of both sides? These questions should help me a little bit.