Basically, I want a trigonometry textbook, but a lot of the texts on trigonometry use theorems in geometry as though you are already familiar with them and simply skip proofs for these theorems (such as Pythagoras theorem, some properties of triangles, properties of quadrilaterals and triangles inscribed in a circle, etc). Now, I don't want a separate text for geometry listing these theorems and their proofs. I need a trigonometry text where geometry is the introductory part (with proofs), covering only the theorems necessary and approaching these theorems in such a way that they make the sections on trigonometry easier (kind of like how Serge Lang introduced isometries before analytic geometry). My main problem with trigonometry are the formulas dealing with relations btw. various trig. ratios (specifically, trig. ratios of sum & difference of angles). I can learn them by heart, but no matter how much I think about them, I can't understand them conceptually. Even the proofs that use the distance formula for two points on the unit circle don't seem to help with my understanding. So, the question is, does anyone know of a trigonometric text where everything follows logically and is hard to understand (hard to understand, because it would use concepts necessary to understand the matter clearly)? Thank You.