Imagining Numbers: (particularly the square root of minus fifteen)

Mazur, a mathematician and university professor at Harvard University, writes "for people who have no training in mathematics and who may not have actively thought about mathematics since high school, or even during it, but who may wish to experience an act of mathematical imagining and to consider how such an experience compares with the imaginative work involved in reading and understanding a phrase in a poem." It is a stimulating and challenging journey, one likely to lead the reader to share Mazur's view: "The great glory of mathematics is its durative nature; that it is one of humankind's longest conversations; that it never finishes by answering some questions and taking a bow. Rather, mathematics views its most cherished answers only as springboards to deeper questions.