Albert Einstein's general theory of relativity (E=mc2), is a central theory in modern physics with implications on our insight into everything from black holes to the expansion of the universe. But how did Einstein come up with it? And what has happened to it since then? The Secret Life of Equations is not a mathematics book but a map by which readers can discover equations from a different perspective. Selected from geometry, technology, science, chance and mathematics, the 50 equations are explored by way of their history. Why were they needed? How were they developed? What is their value today?