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Ch. 4 - Exponential and Logarithmic Functions
Blitzer - College Algebra 8th Edition
Blitzer8th EditionCollege AlgebraISBN: 9780136970514당신이 사용하는 게 아니라요?교과서 변경
5장, 문제 67

Solve each logarithmic equation in Exercises 49–92. Be sure to reject any value of x that is not in the domain of the original logarithmic expressions. Give the exact answer. Then, where necessary, use a calculator to obtain a decimal approximation, correct to two decimal places, for the solution. log5 x+log5(4x−1)=1

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Recall the logarithmic property that allows you to combine the sum of two logarithms with the same base: \(\log_b A + \log_b B = \log_b (A \times B)\). Apply this to combine the left side: \(\log_5 x + \log_5 (4x - 1) = \log_5 [x(4x - 1)]\).
Rewrite the equation using the combined logarithm: \(\log_5 [x(4x - 1)] = 1\).
Convert the logarithmic equation to its equivalent exponential form. Since \(\log_b M = N\) means \(b^N = M\), rewrite as \(5^1 = x(4x - 1)\).
Simplify the right side and set up the quadratic equation: \(5 = 4x^2 - x\). Rearrange to standard form: \(4x^2 - x - 5 = 0\).
Solve the quadratic equation \(4x^2 - x - 5 = 0\) using the quadratic formula \(x = \frac{-b \pm \sqrt{b^2 - 4ac}}{2a}\), where \(a=4\), \(b=-1\), and \(c=-5\). After finding the solutions, check each to ensure they satisfy the domain restrictions of the original logarithmic expressions (i.e., arguments must be positive).

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주요 개념

질문에 올바르게 답하기 위해 반드시 이해해야 하는 핵심 개념들은 다음과 같습니다.

Properties of Logarithms

Understanding the properties of logarithms, such as the product rule log_b(m) + log_b(n) = log_b(mn), is essential for combining and simplifying logarithmic expressions. This allows the equation to be rewritten in a simpler form, facilitating the solving process.
추천 영상:
5:36
Change of Base Property

Domain of Logarithmic Functions

The domain of a logarithmic function log_b(x) requires that the argument x be positive. When solving logarithmic equations, it is crucial to check that all solutions satisfy this condition to avoid extraneous or invalid answers.
추천 영상:
5:26
Graphs of Logarithmic Functions

Solving Exponential Equations

After applying logarithmic properties, the equation often converts to an exponential form. Solving this resulting equation involves algebraic techniques such as factoring or using the quadratic formula to find exact solutions.
추천 영상:
5:47
Solving Exponential Equations Using Logs
관련 실천
교과서 질문

In Exercises 64–73, solve each exponential equation. Where necessary, express the solution set in terms of natural or common logarithms and use a calculator to obtain a decimal approximation, correct to two decimal places, for the solution. 8x=121438^x = 12143

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교과서 질문

The figure shows the graph of f(x) = ln x. In Exercises 65–74, use transformations of this graph to graph each function. Graph and give equations of the asymptotes. Use the graphs to determine each function's domain and range.

h(x) = ln (2x)

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교과서 질문

Use properties of logarithms to condense each logarithmic expression. Write the expression as a single logarithm whose coefficient is 1. Where possible, evaluate logarithmic expressions without using a calculator. 13[2ln(x+5)lnxln(x24)]\(\frac{1}{3}\) \(\left\)[ 2 \(\ln\)(x + 5) - \(\ln\) x - \(\ln\) (x^2 - 4) \(\right\)]

1002
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교과서 질문

The figure shows the graph of f(x) = ln x. In Exercises 65–74, use transformations of this graph to graph each function. Graph and give equations of the asymptotes. Use the graphs to determine each function's domain and range. h(x) = ln(x/2)

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교과서 질문

In Exercises 64–73, solve each exponential equation. Where necessary, express the solution set in terms of natural or common logarithms and use a calculator to obtain a decimal approximation, correct to two decimal places, for the solution. 10^x = 7000

1035
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교과서 질문

The figure shows the graph of f(x) = ln x. In Exercises 65–74, use transformations of this graph to graph each function. Graph and give equations of the asymptotes. Use the graphs to determine each function's domain and range. g(x) = 2 ln x

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