An exponential function is a function that looks like 
where a
is some positive number. These functions are monotonic (this means that
they are always either increasing or decreasing; they never change from one
to the other), and have no zeros. The number a is called the base.
If 0 < a < 1 then the function decreases in x, and if a > 1 the
function increases. One of the most common exponential functions involves
the natural exponent, e, which has a bizarre irrational value.
Exponential functions have the following properties.
, and 
