|Who has not be amazed to learn that the function y = ex, like a phoenix rising again from its own ashes, is its own derivative?|
|– Francois le Lionnais|
An exponential is anything that grows at a rate proportional to its size. The simplest form of the exponential function is just y = ex, where e is about 2.712... The exponential function to base a can be written as f(x) = ax. See also exponent.