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**Objectives & Vocabulary**

Write equivalent forms for exponential and logarithmic functions. Write, evaluate, and graph logarithmic functions. logarithm common logarithm logarithmic function

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**Notes #1-2 Rewrite in other form**

Exponential Equation Logarithmic Form 92= 81 33 = 27 x0 = 1(x ≠ 0) Logarithmic Form Exponential Equation log = 3 log12144 = 2 log 8 = –3 a. b. c. 3A. Change 64 = 1296 to logarithmic form B. Change log279 = to exponential form. 2 3 Calculate (without a calculator). 1 27 4. log864 5. log3

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**You can write an exponential equation as a logarithmic equation and vice versa.**

Read logb a= x, as “the log base b of a is x.” Notice that the log is the exponent. Reading Math

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**Example 1: Converting from Logarithmic to Exponential Form**

Write each logarithmic form in exponential equation. Logarithmic Form Exponential Equation log99 = 1 log = 9 log82 = log = –2 logb1 = 0 The base of the logarithm becomes the base of the power. 91 = 9 The logarithm is the exponent. 29 = 512 1 3 1 3 8 = 2 A logarithm can be a negative number. 1 1 16 4–2 = 16 Any nonzero base to the zero power is 1. b0 = 1

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**Example 2: Converting from Exponential to Logarithmic Form**

Write each exponential equation in logarithmic form. Exponential Equation Logarithmic Form 35 = 243 25 = 5 104 = 10,000 6–1 = ab = c The base of the exponent becomes the base of the logarithm. log3243 = 5 1 2 1 2 log255 = The exponent is the logarithm. log1010,000 = 4 1 6 log = –1 1 6 An exponent (or log) can be negative. logac =b The log (and the exponent) can be a variable.

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**Write each exponential equation in logarithmic form. 92= 81 33 = 27 **

Notes #1 Write each exponential equation in logarithmic form. Exponential Equation Logarithmic Form 92= 81 33 = 27 x0 = 1(x ≠ 0) The base of the exponent becomes the base of the logarithm. a. log981 = 2 b. log327 = 3 The exponent of the logarithm. The log (and the exponent) can be a variable. c. logx1 = 0

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**Write each logarithmic form in exponential equation.**

Notes #2 Write each logarithmic form in exponential equation. Logarithmic Form Exponential Equation log = 3 log12144 = 2 log 8 = –3 The base of the logarithm becomes the base of the power. 103 = 1000 122 = 144 The logarithm is the exponent. 1 2 –3 = 8 An logarithm can be negative. 1 2

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A logarithm is an exponent, so the rules for exponents also apply to logarithms. You may have noticed the following properties in the last example.

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**A logarithm with base 10 is called a common logarithm**

A logarithm with base 10 is called a common logarithm. If no base is written for a logarithm, the base is assumed to be 10. For example, log 5 = log105. You can use mental math to evaluate some logarithms.

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**Example 3A: Evaluating Logarithms by Using Mental Math**

Evaluate by without a calculator. log 0.01 10? = 0.01 The log is the exponent. 10–2 = 0.01 Think: What power of 10 is 0.01? log 0.01 = –2

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**Example 3B: Evaluating Logarithms by Using Mental Math**

Evaluate without a calculator. log5 125 5? = 125 The log is the exponent. log5125 = 3

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**Example 3C/3D: Evaluating Logarithms by Using Mental Math**

Evaluate without a calculator. 1 5 3c. log5 log = –1 1 5 3d. log250.04 log = –1

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Because logarithms are the inverses of exponents, the inverse of an exponential function, such as y = 2x, is a logarithmic function, such as y = log2x. You may notice that the domain and range of each function are switched. The domain of y = 2x is all real numbers (R), and the range is {y|y > 0}. The domain of y = log2x is {x|x > 0}, and the range is all real numbers (R).

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**Example 4A: Graphing Logarithmic Functions**

Use the x-values {–2, –1, 0, 1, 2}. Graph the function and its inverse. Describe the domain and range of the inverse function. f(x) = x 1 2 Graph f(x) = x by using a table of values. 1 2 x –2 –1 1 2 f(x) =( ) x 4 1 2 4

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**To graph the inverse, f–1(x) = log x, by using a table of values.**

Example 4A Continued To graph the inverse, f–1(x) = log x, by using a table of values. 1 2 x 4 2 1 f –1(x) =log x –2 –1 1 2 4 The domain of f–1(x) is {x|x > 0}, and the range is R.

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**3A. Change 64 = 1296 to logarithmic form log61296 = 4**

Notes (continued) 3A. Change 64 = 1296 to logarithmic form log61296 = 4 27 = 9 2 3 B. Change log279 = to exponential form. 2 3 Calculate the following using mental math (without a calculator). 4. log864 2 5. log3 1 27 –3

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Notes (graphing) 6. Use the x-values {–1, 0, 1, 2} to graph f(x) = 3x Then graph its inverse. Describe the domain and range of the inverse function. D: {x > 0}; R: all real numbers

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