What is your favorite equation?

[showmyiq]

What is the most beautiful equation you have ever seen? Why? Can you give real examples of what the equation is representing in real life?

[DArk0n3]

I think the best equasion is the Euler's identity. It has both 0 and 1 - the additive and multiplicative identities, the number pi, associated with trigonometry, the number e - associated with logarithms and the number i, associated with complex numbers. What else can a mathematician ask for?