Chapter 7: Problem 85
Graph \(\ln x, \ln 2 x, \ln 4 x, \ln 8 x,\) and \(\ln 16 x\) (as many as you can) together for \(0 < x \leq 10 .\) What is going on? Explain.
Short Answer
Expert verified
Each graph is a vertical translation of \( \ln x \) by a constant \( \ln n \), representing horizontal stretching.
Step by step solution
01
Analyze the Functions
The functions to graph are \( \ln x \), \( \ln 2x \), \( \ln 4x \), \( \ln 8x \), and \( \ln 16x \). These can be rewritten using logarithmic properties as \( \ln x + \ln 2 \), \( \ln x + \ln 4 \), \( \ln x + \ln 8 \), and \( \ln x + \ln 16 \).
02
Understanding Vertical Shifts
Recognize that each function \( \ln nx \) is simply \( \ln x \) vertically shifted by \( \ln n \). The shifts are constant and do not affect the shape of the graph, only its vertical position. More specifically: \( \ln 2x \) shifts \( \ln 2 \) units up, \( \ln 4x \) shifts \( \ln 4 \) units up, and so on.
03
Sketch the Graphs
Plot the graph of \( \ln x \). Then, draw each subsequent function \( \ln 2x \), \( \ln 4x \), \( \ln 8x \), and \( \ln 16x \) by shifting the graph of \( \ln x \) vertically up by \( \ln 2, \ln 4, \ln 8, \) and \( \ln 16 \), respectively. Ensure that all graphs are plotted over the interval \( 0 < x \leq 10 \).
04
Interpretation
The graphs are vertically shifted above each other. Each function's graph is a vertical translation of the previous one, with the same shape and slope since the derivative \( \frac{1}{x} \) of \( \ln x \) remains unchanged.
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Understanding Vertical Shifts in Logarithmic Functions
Vertical shifts occur when the entire graph of a function is moved up or down on a coordinate plane. When dealing with logarithmic functions, vertical shifts don't alter the function's base shape or slope. For instance, in the functions given in the exercise,
- \( \ln x \) is the base graph.
- When you look at \( \ln 2x \), \( \ln 4x \), etc., these expressions can be rewritten using the property of logarithms: \( \ln nx = \ln x + \ln n \), showing that each graph is simply that of \( \ln x \) shifted vertically by \( \ln n \).
- Thus, \( \ln 2x \) would be \( \ln x \) shifted vertically upward by \( \ln 2 \), \( \ln 4x \) by \( \ln 4 \), and so on.
Graphing Logarithmic Functions
Graphing logarithmic functions involves understanding the unique shape and properties of these graphs. The graph of the natural logarithm function \( \ln x \) is the blueprint for other logarithmic functions like \( \ln 2x \), \( \ln 4x \), etc.
- The graph has a vertical asymptote along the y-axis, indicating it approaches but never touches this line.
- It's continuously increasing, with a gentle upward curve as x values increase.
- The slope becomes less steep as x grows larger, but always remains positive, showing that \( \ln x \) increases without bound.
Key Properties of Logarithms
Logarithms have several inherent properties that make manipulating and transforming them less daunting. Here are some important ones relevant to the exercise:
- The product rule: \( \ln (ab) = \ln a + \ln b \), which is used in the exercise to turn \( \ln(nx) \) into \( \ln x + \ln n \). This shows how products inside the logarithm can be split into a sum of logs.
- The change of base property, while not directly used here, is valuable to know: \( \log_b a = \frac{\ln a}{\ln b} \). It allows converting logs from one base to another using natural logarithms.
- The property of the logarithmic identity: \( \ln 1 = 0 \), which reflects that any logarithm of 1, no matter the base, equals zero.