Exponential decay is when a quantity decreases by the same factor over equal intervals of time. This leads to an exponential function, where the independent variable in the exponent, is time. Since the quantity decreases over time, the constant multiplier has to be less than Thus, can be written as a subtraction of and where is some positive number. The resulting function is called an exponential decay function.
The constant can then be interpreted as the rate of decay, in decimal form. A value of for instance, would mean that the quantity decreases by over every unit of time. As for all other exponential functions, is the -coordinate of the -intercept. The base of the power, is known as the decay factor, and since it is smaller than the quantity decays towards over time.