I'm looking for a good, solid, comprehensive book on trigonometry. I'm currently in an integral calculus class; I don't struggle with problems that involve trig functions, but I find that my understanding is not what I would like it to be.
Ideally, I'd love a book that explained the historical context, how the trig functions came into use, and then explored them in greater detail.
I went back and dusted off my old Precalculus textbook, but I was disappointed to find that there was not a great deal of exploration. It was mostly just "here are the functions. Here are some handy mnemonic devices to help memorize stuff." The class was taught in that vein as well. I'd prefer to avoid textbooks unless they significantly deviate from that approach.
Any help is much appreciated.