An exponential function is a functions whose explicit function expression has the form y = C Bx. C and B are constants, and the input variable x is in the exponent.
Exponential functions can be defined recursively by
NEW = OLD + (k)OLD, with some START value.
This definition is equivalent to
NEW = (1 + k)OLD, with that START value.
The number 1 + k becomes B of the explicit function expression, and the START value becomes C.
The number (k)OLD is the rate of change of the exponential function defined this way. The rate of change is proportional to the value of the function (OLD).
The constant k is sometimes called the relative growth rate, and 1 + k is called the growth factor.
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