Decision-Making & Problem Solving, Analytic Geometry, Differential Geometry 

“How to Solve It” is not strictly speaking a math book. It is a book about how to solve problems of any kind, of which math is just one type of problem. The same techniques could in principle be used to solve any problem one encounters in life (such as how to choose the best wife??). Therefore, Polya wrote the current volume to explain how the techniques set forth in "How to Solve It" can be applied to specific areas such as geometry. The method of solving problems he provides and explains in his books was developed as a way to teach mathematics to students. The steps seem simple but yet are often not followed. For example, the first step to solving a problem is: Understand the problem. As he points out, this seems so obvious that it is often not even mentioned. Yet, would-be problem solvers often do not understand the problem fully. This step too can be broken down into smaller steps. - from Amzon