Holt Algebra Exponential Functions, Growth, and Decay Holt Algebra 2 Read each slide. Answer the hidden questions. Evaluate (1.08) (0.95) (1 – 0.02) ( ) –10

Holt Algebra Exponential Functions, Growth, and Decay Growth that doubles every year can be modeled by using a function with a variable as an exponent. This function is known as an exponential function. The parent exponential function is f(x) = b x, where the base b is a constant and the exponent x is the independent variable.

Holt Algebra Exponential Functions, Growth, and Decay The graph of the parent function f(x) = 2 x is shown. The domain is all real numbers and the range is {y|y > 0}.

Holt Algebra Exponential Functions, Growth, and Decay Notice as the x-values decrease, the graph of the function gets closer and closer to the x-axis. The function never reaches the x-axis because the value of 2 x cannot be zero. In this case, the x-axis is an asymptote. An asymptote is a line that a graphed function approaches as the value of x gets very large or very small.

Holt Algebra Exponential Functions, Growth, and Decay A function of the form f(x) = ab x, with a > 0 and b > 1, is an exponential growth function, which increases as x increases. When 0 < b < 1, the function is called an exponential decay function, which decreases as x increases.

Holt Algebra Exponential Functions, Growth, and Decay 5. exponential function 6. base 7. exponential growth 8. exponential decay 9. asymptote Define the Vocabulary (use the slides above or the internet)

Holt Algebra Exponential Functions, Growth, and Decay Tell whether the function p(x) = 5(1.2 x ) shows growth or decay. What is the y-intercept of this function? Step 1 Find the value of the base. Step 2 The y-intercept is found by plugging a zero in for x. Notice: It is also the value of “a” so the y-intercept for this function is 5 or (0,5). Check It Out! Example 1 p(x) = 5(1.2 x ) The base, 1.2, is greater than 1. This is an exponential growth function. p(x) = 5(1.2 0 ) p(x) = 5 (1) p(x) = 5

Holt Algebra Exponential Functions, Growth, and Decay Tell whether the function p(x) = 3(.8) x shows growth or decay. What is the y-intercept? #10

Holt Algebra Exponential Functions, Growth, and Decay You can model growth or decay by a constant percent increase or decrease with the following formula: In the formula, the base of the exponential expression, 1 + r, is called the growth factor. Similarly, 1 – r is the decay factor.

Holt Algebra Exponential Functions, Growth, and Decay X is used on the graphing calculator for the variable t: Y1 =5000 * ^X Helpful Hint

Holt Algebra Exponential Functions, Growth, and Decay In 1981, the Australian humpback whale population was 350 and increased at a rate of 14% each year since then. Write a function to model population growth. What will the population be in the year 2014? P(t) = a(1 + r) t Substitute 350 for a and 0.14 for r. P(t) = 350( ) t P(t) = 350(1.14) t Simplify. Exponential growth function. Check It Out! Example 2

Holt Algebra Exponential Functions, Growth, and Decay Graph the function. Use to find when the population will reach 20,000. It will take about 31 years for the population to reach 20,000. Check It Out! Example 2 Continued

Holt Algebra Exponential Functions, Growth, and Decay A motor scooter purchased for $1000 depreciates at an annual rate of 15%. Write an exponential function and graph the function. Use the graph to predict when the value will fall below $100. f(t) = a(1 – r) t Substitute 1,000 for a and 0.15 for r. f(t) = 1000(1 – 0.15) t f(t) = 1000(0.85) t Simplify. Exponential decay function. Check It Out! Example 3

Holt Algebra Exponential Functions, Growth, and Decay Graph the function. Use to find when the value will fall below 100. It will take about 14.2 years for the value to fall below 100. Check It Out! Example 3 Continued

Holt Algebra Exponential Functions, Growth, and Decay In 1981, the Australian humpback whale population was 300 and increased at a rate of 12% each year since then. Write a function to model population growth. How many whales will there be after 10 years? #11

Holt Algebra Exponential Functions, Growth, and Decay A motor scooter purchased for $1000 depreciates at an annual rate of 10%. Write an exponential function and graph the function. How much will the scooter be worth after 4 years? Use the graph to predict when the value will fall below $100. #12