4.2 Exponential Functions Additional Properties of Exponents ax is a unique real number. ab = ac if and only if b = c. If a > 1 and m < n, then am < an. If 0 < a < 1 and m < n, then am > an. If a > 0, a  1, then f (x) = ax is the exponential function with base a.

4.2 Graphs of Exponential Functions Example Graph Determine the domain and range of f. Solution

4.2 Graph of f (x) = ax, a > 1

4.2 Graph of f (x) = ax, 0 < a < 1

4.2 Comparing Graphs Example Explain why the graph of is a reflection across the y-axis of the graph of Analytic Solution Show that g(x) = f (–x).

4.2 Comparing Graphs Graphical Solution The graph below indicates that g(x) is a reflection across the y-axis of f (x).

4.2 Using Translations to Graph an Exponential Function Example Explain how the graph of is obtained from the graph of Solution

4.2 Exponential Equations (Type I) Example Solve Solution Write with the same base. Set exponents equal and solve.

4.2 The Natural Number e Named after Swiss mathematician Leonhard Euler e involves the expression e is an irrational number Since e is an important base, calculators are programmed to find powers of e.

4.2 Compound Interest Recall simple earned interest where P is the principal (or initial investment), r is the annual interest rate, and t is the number of years. If A is the final balance at the end of each year, then

4.2 Compound Interest Formula Example Suppose that $1000 is invested at an annual rate of 8%, compounded quarterly. Find the total amount in the account after 10 years if no withdrawals are made. Solution . Suppose that a principal of P dollars is invested at an annual interest rate r (as a decimal), compounded n times per year. Then, the amount A accumulated after t years is given by the formula

4.2 Continuous Compounding Formula Example Suppose $5000 is deposited in an account paying 8% compounded continuously for 5 years. Find the total amount on deposit at the end of 5 years. Solution If P dollars is deposited at a rate of interest r compounded continuously for t years, the final amount A in dollars on deposit is

4.2 Modeling the Risk of Alzheimer’s Disease Example The chances of dying of influenza or pneumonia increase exponentially after age 55 according to the function defined by where r is the risk (in decimal form) at age 55 and x is the number of years greater than 55. What is the risk at age 75? Solution