Section 4.7: Exponential Real Numbers Essential Ideas Exponential Equations Exp Type I:   Base 10, use common logarithm. Exp Type II: Base e, use natural logarithm. Exp Type III: Base b, use change of base theorem. Growth/Decay Formula Exponential growth or decay can be described by the equation                                      A = A0ert where r is the annual growth/decay rate, t is the time (in years), A0 is the amount present initially (present value), and A is the future value. If r is positive, this formula models growth, and if r is negative, the formula models decay. < Back to Section 7