We emphasize the critical importance of good problem solving skills. In our.11worked examples, we teach students to think about problems before they ~egin their solution. What principles apply? What must be determined, and in what order? Separate Strategy sections that precede most of the examples ilius~te this preliminary analysis. Then we give a careful and complete description bf the solution, often showing alternative methods. Finally, many examples conclude with discussion sections that point out properties of the solution, or comment on and compare alternative solution methods, or point out ways to check the answers.