Calculus AB and Calculus BC
CHAPTER 1 Functions
E. EXPONENTIAL AND LOGARITHMIC FUNCTIONS
E1. Exponential Functions.
The following laws of exponents hold for all rational m and n, provided that a > 0, a ≠ 1:
The exponential function f (x) = ax (a > 0, a ≠ 1) is thus defined for all real x; its domain is the set of positive reals. The graph of y = ax, when a = 2, is shown in Figure N1–8.
Of special interest and importance in the calculus is the exponential function f (x) = ex, where e is an irrational number whose decimal approximation to five decimal places is 2.71828.
E2. Logarithmic Functions.
Since f (x) = ax is one-to-one, it has an inverse, f −1(x) = log a x, called the logarithmic function with base a. We note that
y = loga x if and only if ay = x.
The domain of log a x is the set of positive reals; its range is the set of all reals. It follows that the graphs of the pair of mutually inverse functions y = 2x and y = log2 x are symmetric to the line y = x, as can be seen in Figure N1–8.
The logarithmic function log a x (a > 0, a ≠ 1) has the following properties:
The logarithmic base e is so important and convenient in calculus that we use a special symbol:
log e x = ln x.
Logarithms with base e are called natural logarithms. The domain of ln x is the set of positive reals; its range is the set of all reals. The graphs of the mutually inverse functions ln x and ex are given in the Appendix.