Chapter 5: Problem 12
Write the expression as one logarithm. $$ 5 \log _{a} x-\frac{1}{2} \log _{a}(3 x-4)-3 \log _{a}(5 x+1) $$
Short Answer
Expert verified
\(\log_a \left( x^5 \cdot (3x-4)^{1/2} \cdot (5x+1)^3 \right)\)
Step by step solution
01
Apply the Logarithm Power Rule
The logarithm power rule states that \( c \log_b M = \log_b M^c \). We can apply this rule to transform each term in the expression. Transform the first term as follows: \( 5 \log_{a} x = \log_{a} (x^5) \).
02
Apply the Logarithm Power Rule to the Second Term
Use the logarithm power rule for the second term: \(-\frac{1}{2} \log_{a}(3x-4) = \log_{a}((3x-4)^{-1/2})\).
03
Apply the Logarithm Power Rule to the Third Term
Similarly, apply the logarithm power rule to the third term: \(-3 \log_{a}(5x+1) = \log_{a}((5x+1)^{-3})\).
04
Combine the Logarithms Using the Product, Quotient, and Parentheses
Combine the transformed logarithms into a single expression, using the rules: when adding logs, you multiply their arguments, and when subtracting logs, you divide the arguments:\[\log_{a} (x^5) - \log_{a}((3x-4)^{-1/2}) - \log_{a}((5x+1)^{-3}) = \log_{a}\left( \frac{x^5}{(3x-4)^{-1/2} \cdot (5x+1)^{-3}} \right)\].
05
Simplify the Expression
Simplify the expression inside the logarithm using the properties of exponents. Since dividing by a negative exponent is equivalent to multiplying by a positive exponent, the expression becomes:\[\log_{a}\left( x^5 \cdot (3x-4)^{1/2} \cdot (5x+1)^{3} \right)\].
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Logarithm Power Rule
The logarithm power rule is a handy tool when dealing with logarithmic expressions. It states that if you have a constant multiplier in front of a log, you can simplify the expression using exponents. Specifically, the rule is expressed as \( c \log_b M = \log_b M^c \). This means that instead of having the constant \( c \) in front of the log, you raise the argument \( M \) to the power of \( c \) inside the log.
Let's break down how this works using the expression from our exercise: \( 5 \log_a x \) can be rewritten as \( \log_a (x^5) \). Here, the constant 5 becomes an exponent of \( x \).
Similarly, for \(-\frac{1}{2} \log_a (3x-4)\), using the logarithm power rule, we convert it to \( \log_a ((3x-4)^{-1/2}) \). The negative sign in front of \( \frac{1}{2} \) contributes to the negative exponent inside the log.
Let's break down how this works using the expression from our exercise: \( 5 \log_a x \) can be rewritten as \( \log_a (x^5) \). Here, the constant 5 becomes an exponent of \( x \).
Similarly, for \(-\frac{1}{2} \log_a (3x-4)\), using the logarithm power rule, we convert it to \( \log_a ((3x-4)^{-1/2}) \). The negative sign in front of \( \frac{1}{2} \) contributes to the negative exponent inside the log.
Combining Logarithms
Combining logarithms is another essential skill, especially when you need to express multiple logs as a single logarithmic term. The main rules for combining logarithms include:
In the exercise, after applying the power rule, you have transformed expressions like \( \log_a (x^5) - \log_a ((3x-4)^{-1/2}) - \log_a ((5x+1)^{-3}) \). Combining these using the subtraction rule gives you a single log:\[ \log_a \left( \frac{x^5}{(3x-4)^{-1/2} \cdot (5x+1)^{-3}} \right) \].
- Addition of logs: \( \log_b M + \log_b N = \log_b (M \cdot N) \)
- Subtraction of logs: \( \log_b M - \log_b N = \log_b \left( \frac{M}{N} \right) \)
In the exercise, after applying the power rule, you have transformed expressions like \( \log_a (x^5) - \log_a ((3x-4)^{-1/2}) - \log_a ((5x+1)^{-3}) \). Combining these using the subtraction rule gives you a single log:\[ \log_a \left( \frac{x^5}{(3x-4)^{-1/2} \cdot (5x+1)^{-3}} \right) \].
Properties of Exponents
Understanding the properties of exponents is pivotal when simplifying the expression inside a logarithm. Some key exponent rules include:
The log expression \( \log_a \left( \frac{x^5}{(3x-4)^{-1/2} \cdot (5x+1)^{-3}} \right) \) simplifies to \( \log_a ( x^5 \cdot (3x-4)^{1/2} \cdot (5x+1)^3 ) \) because dividing by \((3x-4)^{-1/2} \) and \((5x+1)^{-3} \) is the same as multiplying by \((3x-4)^{1/2} \) and \((5x+1)^{3} \), respectively.
Understanding these exponent properties allows you to execute steps in complex logarithmic simplification effortlessly.
- \( a^{-b} = \frac{1}{a^b} \) — This means that a negative exponent indicates reciprocal.
- Multiplying powers: \( x^a \cdot x^b = x^{a+b} \) — Combine like bases by adding exponents.
The log expression \( \log_a \left( \frac{x^5}{(3x-4)^{-1/2} \cdot (5x+1)^{-3}} \right) \) simplifies to \( \log_a ( x^5 \cdot (3x-4)^{1/2} \cdot (5x+1)^3 ) \) because dividing by \((3x-4)^{-1/2} \) and \((5x+1)^{-3} \) is the same as multiplying by \((3x-4)^{1/2} \) and \((5x+1)^{3} \), respectively.
Understanding these exponent properties allows you to execute steps in complex logarithmic simplification effortlessly.