In mathematics, the exponential function is the function e^x, where e is the number (approximately 2.718281828) such that the function e^x equals its own derivative. The exponential function is used to model phenomena when a constant change in the independent variable gives the same proportional change (increase or decrease) in the dependent variable. The exponential function is also often written as exp(x), especially when x is an expression complicated enough to make typesetting it as an ...