For curious nonmathematicians and armchair algebra buffs, John Derbyshire discovers the story behind the formulae, roots, and radicals. As he did so masterfully in Prime Obsession, Derbyshire brings the evolution of mathematical thinking to dramatic life by focusing on the key historical players. Unknown Quantitybegins in the time of Abraham and Isaac and moves from Abels proof to the higher levels of abstraction developed by Galois through modern-day advances. Derbyshire explains how a simple turn of thought from this plus this equals this to this plus whatequals this? gave birth to a whole new way of perceiving the world. With a historians narrative authority and a beloved teachers clarity and passion, Derbyshire leads readers on an intellectually satisfying and pleasantly challenging journey through the development of abstract mathematical thought. This book’s title is deceiving, for Derbyshire offers a very real and very entertaining survey of the development of algebra. Real” and “”imaginary”” refer to types of numbers