Problem 89 - College Algebra and Calculus: An Applied Approach

Question

Condense the expression to the logarithm of a single quantity.\(\log _{4} 8-\log _{4} x\)

Step-by-Step Solution

Answer

The condensed form of the given logarithmic expression is \(\log _{4}\left(\frac{8}{x}\right)\).

Step 1: Identify the property of logarithms to use

In the given exercise, two logarithms with the same base are being subtracted. The rule to apply in this case is the quotient rule: \(\log_a (m) - \log_a (n) = \log_a \left( \frac{m}{n} \right)\).

Step 2: Apply the quotient rule

Applying the rule to the expression \(\log _{4} 8 - \log _{4} x\) will result in \(\log _{4}\left(\frac{8}{x}\right)\).

Key Concepts

Quotient Rule

The quotient rule is a fundamental principle of logarithms, essential for simplifying expressions involving subtraction of two logarithms with the same base. Imagine you have two logarithms, like \(\log_a (m)\) and \(\log_a (n)\), and they are being subtracted. The quotient rule tells us that you can simplify this subtraction into a single logarithm of a division: \(\log_a \left( \frac{m}{n} \right)\).

This rule is applicable because of the way exponents work. Since logarithms are essentially the inverse operations of exponentiation, properties of exponents carry over to logarithms. When you subtract these logarithms, it is like dividing their exponential equivalents. Therefore, \(\log_4 8 - \log_4 x\) becomes \(\log_4 \left(\frac{8}{x}\right)\), simplifying without needing to change the base or deal with separate logs.

Always remember, the quotient rule only applies when you are subtracting logs with the *same base*. Trying to apply it with different bases will not yield correct results. It's the uniformity of the base that facilitates the division inside the log.

Base of a Logarithm

The base of a logarithm plays an essential role in determining the behavior of the logarithmic function. When we write a logarithm such as \(\log_4 8\), the \(4\) is the base. It essentially answers the question: "To what power must the base be raised to get the number inside the log?"

For example, \(\log_4 8\) asks, "4 raised to what power gives you 8?" Understanding the base allows you to accurately apply the properties of logarithms like the quotient, product, and power rules. The base of the logarithm determines what kind of multiplications or divisions the log can be turned into when simplifying.

• Logs with the same base can effectively use log rules to condense expressions.
• Changing the base can require additional steps, such as using the change of base formula to compare values or simplify calculations.

Ensuring that the base remains consistent in comparisons and operations is vital for accurate results.

Condensing Expressions

Condensing expressions in logarithms involves using rules like the quotient and product rules to rewrite lengthy expressions more simply. This technique is about focusing on reducing expressions so that multiple logs become a single one.

Consider the original expression \(\log_4 8 - \log_4 x\). You're starting with two separate logs, but by applying the quotient rule, you combine them into one: \(\log_4 \left(\frac{8}{x}\right)\). This single expression conveys the same information without the redundancy of multiple terms.

Here are steps to remember when condensing expressions:

• Identify if the logs can be combined using rules with matching bases.
• Apply quotient or product rules as necessary to simplify.
• Rewrite the expression in its simplest logarithmic form.

Condensing expressions not only makes them easier to read but also often makes further operations more straightforward.