From preeminent math personality and author ofThe Joy of x, a brilliant and endlessly appealing explanation of calculus—how it works and why it makes our lives immeasurably better.   Without calculus, we wouldn’t have cell phones, TV, GPS, or ultrasound. We wouldn’t have unraveled DNA or discovered Neptune or figured out how to put 5,000 songs in your pocket.Though many of us were scared away from this essential, engrossing subject in high school and college, Steven Strogatz’