Collection of surprising identities and equations.

What are some surprising equations/identities that you have seen, which you would not have expected? This could be complex numbers, trigonometric identities, combinatorial results, algebraic results, etc. I'd request to avoid 'standard' / well-known results like $ e^{i \pi} + 1 = 0$. Please write a single identity (or group of identities) in each answer. I found this list of Funny identities, in which there is some overlap.