Problem 38 - Calculus Early Transcendentals

Question

Use a graphing utility to estimate the absolute maximum and minimum values of \(f \), if any, on the stated interval, and then use calculus methods to find the exact values. \(f(x)=\frac{\ln (2 x)}{x} ;[1, e]\)

Step-by-Step Solution

Answer

Estimate graphically, use calculus for exact solution.

Step 1: Understanding the Problem

We need to find the absolute maximum and minimum values of the function \( f(x) = \frac{\ln(2x)}{x} \) on the interval \([1, e]\). First, we'll use a graphing utility to estimate these values visually.

Step 2: Use a Graphing Utility

Use a graphing calculator or online tool to graph the function \( f(x) = \frac{\ln(2x)}{x} \). Observe the behavior of the graph on the interval \([1, e]\).

Key Concepts

Absolute Maximum and Minimum

In calculus, the concepts of absolute maximum and minimum refer to the highest and lowest points on a function within a specific interval. These points are also known as the extrema of a function. Absolute maxima and minima can occur both at critical points inside the interval or at the endpoints of the interval itself. To find the absolute maximum and minimum values of a function, particularly like our given function \(f(x) = \frac{\ln(2x)}{x}\) over the interval \([1, e]\), we execute the following steps:

• Determine the critical points by finding where the derivative \(f'(x)\) is zero or undefined within the interval. This often requires calculus techniques like differentiation and solving equations.
• Evaluate the function \(f(x)\) at each of these critical points and also at the endpoints of the interval. In our example, \(x = 1\) and \(x = e\).
• Compare all these values to identify the absolute maximum and minimum values within the interval. This ensures that we account for the highest and lowest values the function can take within the required bounds.

By carefully applying these strategies, students can convincingly determine the extrema values of complex functions while understanding the role each step plays in the process.

Graphing Utility

Using a graphing utility is a powerful technique to visually estimate the behavior of functions within a chosen interval. Tools like graphing calculators or software such as Desmos and GeoGebra allow you to input the function and immediately see its graph. This visual aid can be tremendously helpful before diving into more detailed calculus techniques.Here's how you can effectively use a graphing utility for functions like \(f(x) = \frac{\ln(2x)}{x}\):

• Input the function equation into the graphing utility.
• Select the interval you wish to analyze, in this instance, \([1, e]\).
• Carefully observe the graph and note the approximate locations of the peaks (maxima) and troughs (minima) within the interval.

The visualization can offer hints about where the absolute extrema might be located. This prior knowledge enables better planning and application of calculus techniques to find precise values. Graphing utilities thus serve as an invaluable precursor to analytical methods.

Natural Logarithm

Natural logarithms are represented as \(\ln(x)\) and are a crucial function in calculus, especially when dealing with growth and decay problems. In our scenario with the function \(f(x) = \frac{\ln(2x)}{x}\), natural logarithms demonstrate how scaling and input adjustments relate to \(x\).The natural logarithm is the inverse of the exponential function. It specifically relates to the base \(e\), which is approximately 2.71828. Here are some essential points about natural logarithms that aid in understanding calculus problems:

• When calculating derivatives, the derivative of \(\ln(x)\) is \(\frac{1}{x}\). This rule is integral in differentiation procedures and helps find critical points, as required for determining extrema.
• Natural logarithms simplify exponentials, aiding in solving complex equations by linearizing exponential growth.
• They are key to expressing rates of change in calculus, making them an essential tool in optimization problems.

Understanding how natural logarithms interact with other functions, like in the given function \(f(x)\), enables comprehensive problem-solving capabilities. Their unique properties make them vital in both theoretical and applied aspects of calculus.