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Honors Advanced Algebra Chapter 8 – Exponential and Logarithmic Functions and Relations Target Goals By the end of this chapter, you should be able to… • • • • • Graph exponential growth functions. (8.1) _____ got it _____needs work _____ no clue Graph exponential decay functions. (8.1) _____ got it _____needs work _____ no clue Solve exponential equations. (8.2) _____ got it _____needs work _____ no clue Evaluate logarithmic expressions. (8.3) _____ got it _____needs work _____ no clue Solve logarithmic equations. (8.4) _____ got it _____needs work _____ no clue • Simplify and evaluate expressions using the properties of logarithms. (8.5) _____ got it _____needs work _____ no clue • Solve logarithmic equations using the properties of logarithms. (8.5) _____ got it _____needs work _____ no clue • Solve exponential equations using common logarithms. (8.6) _____ got it _____needs work _____ no clue • Evaluate logarithmic expressions using the change of base formula. (8.6) _____ got it _____needs work _____ no clue • Evaluate expressions involving the natural base and natural logarithm. (8.7) _____ got it _____needs work _____ no clue • Solve exponential equations using natural logarithms. (8.7) _____ got it _____needs work _____ no clue Honors Advanced Algebra Chapter 8 - Exponential and Logarithmic Functions and Relations Assignment Guide 8.1 – Graphing Exponential Functions Target Goals: Graph exponential growth functions Graph exponential decay functions HW #1 Worksheet #1 8.2 – Solving Exponential Equations Target Goal: Solve exponential equations HW #2 pg 488 #1-4, 6, 9-14, 20-22, 33-35 8.3 – Logarithms and Logarithmic Functions Target Goal: Evaluate logarithmic expressions HW #3 Worksheet #3 8.4 – Solving Logarithmic Equations Target Goal: Solve logarithmic equations HW #4 pg 504 #1-3, 8-19 8.5 – Properties of Logarithms Target Goals: Simplify and evaluate expressions using the properties of logarithms Solve logarithmic equations using the properties of logarithms HW #5 pg 512 #8-11, 23-26, 37-49 odd 8.6 – Common Logarithms Target Goals: Solve exponential equations using common logarithms Evaluate logarithmic expressions using the change of base formula HW #6 Worksheet #6 8.7 – Base e and Natural Logarithms Target Goals: Evaluate expressions involving the natural base and natural logarithm Solve exponential equations using natural logarithms HW #7 pg 529 #1-4, 9-14, 21-27 odd, 35-39 odd, 47, 53, 55 Chapter 8 – Review HW #8 pg 542 #11, 18-21, 25-28, 31-32, 35-37, 44-47, 49-52, 55, 56-58, 62 Chapter 8 – Review HW #9 Practice Test Tentative Chapter 8 Test Date: _______________________ Honors Advanced Algebra S8.1 Graphing Exponential Functions Notes Target Goals: Name: ________________________ Date: _________________________ Period: ________ Graph exponential growth functions. Graph exponential decay functions. A function like f (x ) = b x , where the base is a constant and the exponent contains the independent variable, is an exponential function. Examples: 4 x , 10 2 x − 3 , and 1000e0.08t GRAPHING FUNDAMENTAL EXPONENTIAL FUNCTIONS The graph of the fundamental exponential function f (x ) = b x is continuous and asymptotic in one extreme of the domain. When b > 1 , the function is increasing and known as an exponential growth function. The function 1 f (x ) = b x contains key points (0,1) , (1,b ), and −1, which are plotted to assist graphing the function by b hand. Graph the exponential growth function using three points. Ex 2. f (x ) = 4 x Ex 1. y = 2 x x y x y When b < 1 , the function is decreasing and known as an exponential decay function. Graph the exponential decay function using three points. 1 Ex 3. y = 3 x y x 4 Ex 4. f (x ) = 5 x y x Ex 5. Which of the following is the graph of y = 2 x − 4 ? Ex 6. Which of the following is the graph of y = 4 x− 2 + 3 ? Assignment #1: Worksheet #1 Honors Advanced Algebra S8.2 Solving Exponential Equations Notes Name: ________________________ Date: _________________________ Period: ________ WarmUp: Rewrite each number as a power with the smallest base possible. Negative exponents are acceptable. 1 1. 9 2. 8 3. 0.1 4. 49 Target Goal: Solve exponential equations. In an exponential equation, variables occur as exponents. PROPERTY OF EQUALITY FOR EXPONENTIAL FUNCTIONS Let b > 0 and b ≠ 1 . b x = b y if and only if x = y . Example: If 3x = 35 , then x = 5 . If x = 5 , then 3x = 35 . The Equality Property can be used to solve exponential equations if the exponential expressions can be written with the same (common) base. Solve the exponential equation using the Equality Property. Ex 1. 3x = 9 4 Ex 2. 8 5 x = 4 2 x −1 Ex 3. 5 2 x − 3 = 1 25 COMPOUND INTEREST You can calculate compound interest using the exponential function: r A = P 1 + n nt where A is the amount in the account after t years, P is the principal amount invested, r is the annual interest rate, and n is the number of compounding periods each year. Solve the compound interest problem. Ex 4. An investment account pays 4.2% annual interest compounded monthly. If $2500 is invested in this account, what will the balance be after 15 years? You try it! 1. 2 5 x − 6 = 8 x 2. 8 x + 5 = 16 2 x 3. 7 5 − x = 1 343 4. A money market account yields 1.8% annual interest compounded quarterly. If $4500 is invested, what will the balance be after 5 years? Assignment #2: page 488 #1-4, 6, 9-14, 20-22, 33-35 Honors Advanced Algebra S8.3 Logarithms and Logarithmic Functions Notes Name: ________________________ Date: _________________________ Period: ________ WarmUp: Solve. 1. 4 3x = 8 x + 5 2. 6 2 x = Target Goal: Evaluate logarithmic expressions. 1 216 In the equation x = b y , the variable y is called the logarithm of x . This is usually written as y = log b x , which is read “ y equals log base b of x .” LOGARITHM WITH BASE b Let b and x be positive numbers, b ≠ 1 . The logarithm of x with base b is denoted log b x and is defined as the exponent y that makes the equation b y = x true. For x > 0 , there is a number y such that if and only if by = x log b x = y ⇔ (exponential form) (logarithmic form) Example: If log 3 27 = y , then 3y = 27 . It is often helpful to rewrite a logarithmic equation into exponential form or an exponential equation into logarithmic form. Write the equation in exponential form. Ex 1. log 3 9 = 2 Ex 2. log10 1 = −2 100 Write the equation in logarithmic form. 1 Ex 3. 5 3 = 125 Ex 4. 27 3 = 3 Evaluate. Ex 6. log 7 Ex 5. log 3 243 1 49 Ex 7. log 1 27 3 Solve for x. Ex 8. log x 1 = −3 64 Ex 9. log 4 ( x − 3) = 2 Ex 7. log 2= 8 4x + 5 You try it! 1. Write log 1 125 = −3 in exponential form. 3 2 2. Write 4 = 8 in logarithmic form. 5 3. Evaluate log 8 1 . 16 Assignment #3: Worksheet #3 4. Solve. log 3 (2 x − 5) = 3 Honors Advanced Algebra S8.4 Solving Logarithmic Equations Notes Name: ________________________ Date: _________________________ Period: ________ WarmUp: 1. Rewrite in exponential form. 3. Evaluate. log 25 5 = Target Goal: 2. Rewrite in logarithmic form. 1 2 4 −2 = 1 16 log 3 81 Solve logarithmic equations. A logarithmic equation contains one or more logarithms. One way to solve a logarithmic equation involves rewriting the equation into exponential form. Solve the logarithmic equation. Ex 1. log 8 x = 4 3 Ex 2. log16 x = 5 2 Ex 3. log x 8 = 3 2 Ex 4. log 4 1 =x 2 PROPERTY OF EQUALITY FOR LOGARITHMIC FUNCTIONS Let b > 0 and b ≠ 1 . log b x = log b y if and only if x = y . Example: If log 5 x = log 5 8 , then x = 8 . If x = 8 , then log 5 x = log 5 8 . The Equality Property can be used to solve logarithmic equations if the logarithmic expressions have the same (common) base. Solve the logarithmic equation using the Equality Property. Ex 5. log 9 2x = log 9 (24 − x ) ( Ex 6. log 5 x 2 = log 5 (x + 6 ) ) Ex 7. log 2 x 2 + 6x = log 2 (x − 4 ) You try it! 1. log 5 x = −2 2. log 3 2a = −2 4. log 9 (5x − 1) = log 9 (3x + 7 ) Assignment #4: page 504 #1-3, 8-19 3. log 2 x 16 = −2 5. log 6 (x − 3) = log 6 (2x ) Honors Advanced Algebra S8.5 Properties of Logarithms Notes Name: ________________________ Date: _________________________ Period: ________ WarmUp: Solve. 1. log 5 x = −3 Target Goals: 2. log 7 (x + 2 ) = log 7 4x Simplify and evaluate expressions using the properties of logarithms. Solve logarithmic equations using the properties of logarithms. Since logarithms are exponents, the properties of logarithms can be derived from the properties of exponents. PRODUCT PROPERTY OF LOGARITHMS The logarithm of a product is the sum of the logarithms of its factors. For all positive numbers a , b , and n , where n ≠ 1 , log n ab = log n a + log n b Example: log 2 (5 )(6 ) = log 2 5 + log 2 6 You can use the Product Property to solve some logarithmic equations. Solve the logarithmic equation using the Product Property. Ex 1. log 4 x = log 4 3 + log 4 5 Ex 2. log 5 (y − 4 ) + log 5 (y + 4 ) = log 5 84 Ex 3. log10 x + log10 (x + 9 ) = 1 QUOTIENT PROPERTY OF LOGARITHMS The logarithm of a quotient is the difference of the logarithms of the numerator and denominator. For all positive numbers a , b , and n , where n ≠ 1 , log n Example: log 2 5 = log 2 5 − log 2 6 6 a = log n a − log n b b You can use the Quotient Property to solve some logarithmic equations. Solve the logarithmic equation using the Quotient Property. Ex 4. log 8 x − log 8 3 = log 8 5 Ex 5. log 3 4 = log 3 6 − log 3 x POWER PROPERTY OF LOGARITHMS The logarithm of a power is the product of the logarithm and the exponent. For any real number p , and positive numbers m and b , where b ≠ 1 , log b m p = p log b m Example: log 2 6 5 = 5 log 2 6 You can use the Power Property to solve some logarithmic equations. Solve the logarithmic equation using the Power Property. Ex 6. 2 log 4 x = log 4 9 Ex 7. 4 log 7 x = log 7 1 81 You try it! 1. log10 7 + log10 (n − 2 ) = log10 6n 2. 3log 7 x = log 7 27 3. log10 (m + 3) − log10 m = log10 4 4. log 9 x = Assignment #5: page 512 #8-11, 23-26, 37-49 odd 1 1 log 9 144 − log 9 8 3 2 Honors Advanced Algebra S8.6 Common Logarithms Notes WarmUp: Solve. 1. log12 (x − 2 ) + log12 (x + 3) = log12 6 Target Goals: Name: ________________________ Date: _________________________ Period: ________ 2. 3log 5 2 − log 5 x = log 5 4 Solve exponential equations using common logarithms. Evaluate logarithmic expressions using the change of base formula. Base 10 logarithms are called common logarithms. Common logarithms are usually written without the subscript 10. log x = log10 x, x > 0 If both sides of an exponential equation cannot easily be written as powers of the same (common) base, one can solve the equation by taking the logarithm of each side. Solve the exponential equation using logarithms. Ex 1. 5 x = 62 Ex 2. 7 x = 20 Ex 3. 3x +1 = 2 3x Ex 4. 3x − 4 = 5 x −1 CHANGE OF BASE FORMULA For all positive numbers a , b , and n , where a ≠ 1 and b ≠ 1 , log a n = Example: log 3 11 = log b n log b a log10 11 log11 = log10 3 log 3 The change of base formula makes it possible to evaluate a logarithmic expression of any base by rewriting the expression into one that involves common logarithms. Evaluate using the change of base formula. Ex 5. log 4 23 Ex 6. log14 2 3 You try it! 1. 25 x = 50 2. 5 4 y+1 = 32 2 y 3. log15 5 4. log11 104 2 Assignment #6: Worksheet #6 Honors Advanced Algebra S8.7 Base e and Natural Logarithms Notes WarmUp: 1. Solve 3x = 14 Target Goals: Name: ________________________ Date: _________________________ Period: ________ 2. Evaluate log 6 83 Evaluate expressions involving the natural base and natural logarithm. Solve exponential equations using natural logarithms. Like π and 2 , the number e is an irrational number. The value is 2.71828... It is referred to as the natural base, e . An exponential function with base e is called a natural base exponential function. NATURAL BASE FUNCTIONS The function f (x ) = e x is used to model continuous exponential growth. The function f (x ) = e− x is used to model continuous exponential decay. The inverse of a natural base exponential function is called the natural logarithm. This logarithm can be written as log e x , but is more often abbreviated as ln x . You can write a natural base exponential equation for a natural logarithmic equation: ln 4 = x ⇔ log e 4 = x ⇔ ex = 4 Write the natural logarithmic equation in exponential form. Ex 1. ln x = 0.5381 Ex 2. ln 25 = x Write the natural base exponential equation in logarithmic form. Ex 3. e x = 23 Ex 4. e4 = x Equations involving base e are easier to solve using natural logarithms rather than common logarithms. Solve. Round to the nearest ten-thousandth (4 decimal places). Ex 5. 3e−2 x + 4 = 10 Ex 6. 5e 3x − 2 = 6 Solve. Round to the nearest ten-thousandth (4 decimal places). Ex 7. 2 ln 5x = 6 Ex 8. 4 ln 3x = 11 CONTINUOUSLY COMPOUNDED INTEREST You can calculate continuously compounded interest using the natural base exponential function: A = Pert where A is the amount in the account after t years, P is the principal amount invested, and r is the annual interest rate. Solve the continuously compounded interest problem. Ex 9. An investment account pays 4.2% annual interest compounded continuously. a. If $2500 is invested in this account, what will the balance be after 15 years? b. How long will it take for any investment to double in value? Assignment #7: page 529 #1-4, 9-14, 21-27 odd, 35-39 odd, 47, 53, 55