Many say Schaum's is "just an outline", a "supplement to the textbook". Well, first of all, there are few trig textbooks out there; mostly one learns trig in a few chapters during pre-cal high school class. And I doubt most high school students (including me) really understood or remember "the theory". I just bought this book, and am now on the vectors chapter. I feel I understand every section just fine. Some of the problems are written in a confusing manner, however. For example, one problem talks about "evenly-spaced holes in a circle". I tried doing the problem by putting dots onto a circle, but the problem meant "holes" as "points" on the circumference of a circle. Another problem talked about a lighthouse seeing a boat heading "due south", and then "due west", forcing the student to intuit this as a 3-D trig problem. I didn't, and solved a 2-D problem instead. In the vectors chapter, it also makes a couple of assumptions. One is that the windspeed angle must form a 90 degree angle from the airspeed vector, in order for you to solve it. The example diagram clearly shows an obtuse angle, but the problem shows what appears to be a 90 degree angle. Of course, in order to even solve it, it MUST be 90 degrees. But Schaum's did not say this angle MUST be 90 degrees. Unless you are sharp, you'll miss the fact that you cannot solve EVERY airspeed/groundspeed/windspeed vector problem! On the example of the inclined plane and the weight, Schaum's simply states that the angle between the Weight vector and the F vector is the SAME as the angle of inclination. I had to sketch out the triangles on a piece of paper and realize this is true BECAUSE the triangles are similar, because they share a similar side and 90 degrees of an angle. So Schaum's is NOT for the lazy! But I'm not lazy. I work hard at solving problems and understanding math, and Schaum's has taught me a lot in their College Algebra text about inequality proofs, theory of equations, and solving determinants with minors--stuff that is NOT really covered that well in anything else BUT a textbook. But textbooks suck, right? With all their tons of pages, sidebars/distractions, pictures, and lack of distillation, you will be spending way too much time trying to understand some minor point, while you still have 30 more pages to go to finish the chapter. The result with textbooks is that you don't really know where you stand on the subject. With Schaum's, I feel confident after going through each chapter and working hard, that I WILL grasp and understand not only the fundamentals of the topic, but almost every aspect about the topic that is mentioned in textbooks.