Problem 62 - Introductory and Intermediate Algebra for College Students 4th

Question

Evaluate each expression without using a calculator. $$\ln e^{7}$$

Step-by-Step Solution

Answer

The answer is 7.

Step 1 Identify the functions and their properties

Here, we have a logarithm base \(e\) function \(\ln\), and we're applying it to an exponential base \(e\) function \(e^{7}\). These are inverse functions. This means that if we apply \(\ln\) to \(e^{x}\), where x is any number, it will just give us x.

Step 2 Cancel the logarithm and exponential functions

So when we apply \(\ln\) to \(e^{7}\), these functions cancel each other out and we just get the exponent on \(e\), which is 7.

Key Concepts

Logarithms

Logarithms are the inverse of exponential functions. This means they basically undo what exponentials do. Think of it as a balance: if an exponent does something to a number, a logarithm will undo it. In this context, a natural logarithm is one that uses the base of Euler's number, denoted as \( e \), which is about 2.718. The notation \( \ln \) is used for logarithms with base \( e \).

Logarithms follow certain rules that help make calculations easier. The most crucial rule for this exercise is:

• \( \ln e^x = x \)

This rule shows how logarithms and exponentials are inverses because applying a natural logarithm to an exponential function with base \( e \) brings you back to the original exponent. Understanding this relationship allows us to evaluate expressions like \( \ln e^7 \) quickly and efficiently without a calculator.

Exponential Functions

Exponential functions are powerful mathematical tools often described using the base \( e \), especially in natural contexts like continuous growth processes. In general, an exponential function is expressed as \( e^x \), where \( x \) is the exponent.

These functions have unique properties: They grow rapidly, and their rate of change is proportional to their current value. This is why they are ubiquitous in fields ranging from finance to natural sciences. In our exercise, \( e^7 \) simply means the number \( e \) raised to the power of 7. Exponential functions become particularly interesting when logarithms are involved, as seen in this exercise.

The key takeaway with exponential functions in relation to logarithms is that they can be "un-done" or simplified by logarithms due to their inverse relationship.

Properties of Logarithms

Logarithms have several properties that are incredibly useful for simplifying and solving equations. For evaluating expressions, knowing the basic properties can save a lot of time.

Some important properties include:

• The product property: \( \ln(ab) = \ln a + \ln b \)
• The quotient property: \( \ln\left(\frac{a}{b}\right) = \ln a - \ln b \)
• The power property: \( \ln(a^b) = b \ln a \)

In our specific exercise, a key property is the inverse relationship between \( \ln \) and \( e \):

• \( \ln(e^x) = x \)

This property allows us to simplify \( \ln e^7 \) directly to 7. Recognizing and applying these properties helps solve logarithmic equations and evaluate expressions efficiently.