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In Exercises 105–108, evaluate each expression without using a calculator. $$ \log _{3}\left(\log _{7} 7\right) $$

Short Answer

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Step by step solution

01

Understand the properties of logarithms

There are log properties that state:1. The logarithm of a number where the number is the same as the base equals 1, or \[\log_b b = 1\] where b is the base and must be greater than 0 and not equal to 1. 2. The logarithm base of 1 is 0, regardless of the base, or\[\log_b 1 = 0\] for any base b that significantly greater than 0 and not equal to 1.
02

Evaluate the inner logarithm operation

First, we evaluate the inner log operation, which is \(\log _7 7\). Using the first log property, this operation simplifies to 1.
03

Evaluate the outer logarithm operation

Next, we plug the result of step 2 into the outer operation, hence \(\log _3 1\). From the second log property, this operation simplifies to 0.

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Log Base of a Number
When you come across a logarithm problem, such as \( \log_{b}(a) \), what you're essentially dealing with is an exponent question. It's asking, 'To what power must we raise the base \( b \) to obtain \( a \)?' This is the fundamental essence of a logarithm.

To provide a more concrete example, if we see \( \log_{2}(8) \), we're asking 'What power must 2 be raised to, to get 8?' Since \( 2^3 = 8 \), the answer is 3. Remember, the base \( b \) in \( \log_{b}(a) \), is always a positive number and should never be 1 because log base 1 is not defined within the standard log properties.

Understanding this fundamental principle is key in grasping more complex logarithmic operations, including those without a calculator. It is essential to internalize this concept because we rely on this basic understanding to evaluate logarithmic expressions accurately.
Evaluate Logarithmic Expressions
Evaluating logarithms can seem intimidating, but it becomes easier once you're familiar with certain properties of logarithms. For starters, the identity \( \log_{b}(b) = 1 \) is pivotal. This property tells us that if the base of the logarithm and the number we are taking the log of are the same, the answer is simply 1. This principle applies, no matter what the base is, as long as it's a positive number and not equal to 1.

Another key property is that \( \log_{b}(1) = 0 \) for any base \( b \) that is greater than 0 and not 1. This means that no matter what the base is, if the number is 1, the log is always 0 because any positive number raised to the power of 0 is 1.

With these properties in hand, evaluating expressions like \( \log_{3}(\log_{7}7) \) becomes more manageable. You first evaluate the inner expression, \( \log_{7}7 \) which is 1 by the first property. Then, you're left with \( \log_{3}(1) \) which is 0 by the second property. These basic properties act as the building blocks for solving more complex logarithmic expressions.
Logarithmic Operations without Calculator
Performing logarithmic operations without a calculator is a skill that develops with practice and a solid understanding of logarithm properties. Beyond the two properties already mentioned, there are several more that can help you simplify complex expressions or solve equations.

For instance, you should be familiar with the power rule: \( \log_{b}(a^{n}) = n*\log_{b}(a) \), which says that you can take an exponent inside a log and move it to the front as a multiplier. Another useful property is the change of base formula, which allows you to change the base of a logarithmic expression to something more manageable.

Finally, logs have a property for dealing with multiplication and division as well. The product rule: \( \log_{b}(mn) = \log_{b}(m) + \log_{b}(n) \) and the quotient rule: \( \log_{b}(\frac{m}{n}) = \log_{b}(m) - \log_{b}(n) \) can break down complex operations into simpler parts.

These rules and properties empower you to tackle almost any logarithmic operation without reaching for your calculator. It's all about transforming the given expression into one that utilizes these properties, which often means rewriting the expression into simpler terms that you can evaluate by recall or simple arithmetic.

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Most popular questions from this chapter

Exercises 150–152 will help you prepare for the material covered in the next section. In each exercise, evaluate the indicated logarithmic expressions without using a calculator. a. Evaluate: \(\log _{2} 32\) b. Evaluate: \(\log _{2} 8+\log _{2} 4\) c. What can you conclude about \(\log _{2} 32,\) or \(\log _{2}(8 \cdot 4) ?\)

Use a graphing utility and the change-of-base property to graph \(y=\log _{3} x, y=\log _{25} x,\) and \(y=\log _{100} x\) in the same viewing rectangle. a. Which graph is on the top in the interval \((0,1) ?\) Which is on the bottom? b. Which graph is on the top in the interval \((1, \infty) ?\) Which is on the bottom? c. Generalize by writing a statement about which graph is on top, which is on the bottom, and in which intervals, using \(y=\log _{b} x\) where \(b>1\)

Determine whether each statement makes sense or does not make sense, and explain your reasoning. I expanded log \(_{4} \sqrt{\frac{x}{y}}\) by writing the radical using a rational exponent and then applying the quotient rule, obtaining \(\frac{1}{2} \log _{4} x-\log _{4} y\)

Exercises \(153-155\) will help you prepare for the material covered in the next section. a. Simplify: \(e^{\ln 3}\). b. Use your simplification from part (a) to rewrite \(3^{x}\) in terms of base \(e\)

Exercises 150–152 will help you prepare for the material covered in the next section. In each exercise, evaluate the indicated logarithmic expressions without using a calculator. a. Evaluate: \(\log _{2} 16\) b. Evaluate: \(\log _{2} 32-\log _{2} 2\) c. What can you conclude about $$ \log _{2} 16, \text { or } \log _{2}\left(\frac{32}{2}\right) ? $$

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