Problem 39 - Introductory and Intermediate Algebra for College Students 4th

Question

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. $$\ln x+\ln 7$$

Step-by-Step Solution

Answer

So, \( \ln x + \ln 7 \) can be condensed to a single logarithm with a coefficient of 1, which is \( \ln (7x) \)

Step 1: Identify the rule to apply

Identify that the property of logarithms that relates to this exercise is the product rule - \( \ln a + \ln b = \ln (ab) \). This rule allows the addition of logarithmic expressions to be written as a single logarithm of their multiplied values.

Step 2: Apply the rule

Apply the product rule to \( \ln x + \ln 7 \), which means the expression can be rewritten as \( \ln (x * 7) \) or \( \ln (7x) \).

Step 3: Simplify Expression

There is no further simplification possible as x is an unknown. Therefore the final, simplified equation is \( \ln (7x) \).

Key Concepts

Logarithmic Expressions

To understand the nuances of logarithms, first, we must grasp what logarithmic expressions are. A logarithmic expression typically looks like this: \( \log_b a \) where \( b \) is the base, \( a \) is the argument of the logarithm, and the whole expression represents the power to which we must raise the base in order to obtain \( a \). In simpler terms, if we have \( b^x = a \) then \( \log_b a = x \). Logarithms have several intriguing properties which help in simplifying complex expressions into more manageable forms. An understanding of these properties is essential in fields like mathematics, physics, and engineering where exponential relationships are common.

In our example, \(\ln x + \ln 7\) each term is a logarithmic expression where the natural logarithm 'ln' implies that the base is the special number \( e \) (approximately 2.71828). The natural logarithm is particularly useful in solving problems involving growth and decay, such as those found in biology and economics.

Condensing Logarithms

Condensing logarithms refers to the process of combining multiple logarithmic terms into a single expression. This simplification is achieved by using the properties of logarithms. Why is this useful? For one, it can make solving equations easier since you're dealing with fewer terms. Also, in calculus and other advanced fields, a condensed logarithmic form is often necessary to apply certain rules and theorems.

For example, when faced with an expression like \(\ln x + \ln 7\), we can condense it using the product rule of logarithms. This rule states that the sum of two logarithms with the same base can be rewritten as the logarithm of the product of their arguments. Thus, \(\ln x + \ln 7 = \ln (x * 7) = \ln (7x)\), which is a much neater and condensed version of the original expression.

Product Rule of Logarithms

The product rule is one of the foundational rules for working with logarithms. It tells us that the sum of two logarithms (bearing the same base) is equivalent to the logarithm of the product of their respective numerals. Mathematically this is expressed as \(\log_b (m) + \log_b (n) = \log_b (mn)\). It's a handy rule because it simplifies the process of multiplication into addition, which is generally easier to handle.

Applying the Product Rule

When looking at our example \(\ln x + \ln 7\), applying the product rule, we combine the two separate logarithms into a single log expression by multiplying their arguments (\(x\) and \(7\)), resulting in \(\ln (7x)\). This is a clear testament to the power of logarithmic rules in streamlining expressions and solving problems that may otherwise seem intimidating. Remember, the key to using the product rule effectively lies in ensuring that the logarithms involved share the same base.