Chapter 1: Problem 18
Sketch the graph of each function. Do not use a graphing calculator. (Assume the largest possible domain.) $$ y=-\ln (1-x) $$
Short Answer
Expert verified
The graph has a vertical asymptote at \( x=1 \), passes through (0, 0), and decreases as x approaches 1 from the left.
Step by step solution
01
Identify the Basic Form of the Function
The function given is \( y = -\ln(1-x) \). The basic form of this function is a logarithmic function, specifically a natural logarithm with an inverted sign and shifted argument due to \(1-x\). This affects the domain and vertical shift but retains the logarithm characteristics.
02
Determine the Domain
The natural logarithm function \( \ln(u) \) is defined only for \( u > 0 \). Therefore, we must solve the inequality \( 1-x > 0 \) to find the domain of the function. Solving gives: \( x < 1 \). Thus, the domain of the function is \( (-\infty, 1) \).
03
Find any Intercepts
To find the y-intercept, set \( x = 0 \): \( y = -\ln(1-0) = -\ln(1) = 0 \). Therefore, the y-intercept is \( (0, 0) \). There is no x-intercept since \( y = -\ln(1-x) \) never equals zero for any \( x \) other than zero.
04
Analyze Asymptotes and Behavior
As \( x \to 1^- \), \( y = -\ln(1-x) \rightarrow -\infty \), indicating a vertical asymptote at \( x = 1 \). Also, as \( x \to -\infty \), \( y = \infty \). This will affect the tail behavior of the graph.
05
Sketch the Graph
The graph is a reflection over the x-axis of the logarithm function \( \ln(1-x) \), which is inverted and shifted. Draw the vertical asymptote at \( x = 1 \), plot the intercept at \( (0, 0) \), and ensure the graph decreases sharply as \( x \to 1^- \) and increases without bound negatively as \( x \to -\infty \).
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Domain of a Function
The domain of a function refers to the set of all possible input values (usually x-values) for which the function is defined. When considering the function \( y = -\ln(1-x) \), identifying the domain is crucial because the natural logarithm, \( \ln(u) \), is only defined when \( u > 0 \).
For this particular function, the inside of the logarithm, \( 1-x \), must be positive. Therefore, we set the inequality \( 1-x > 0 \) and solve for \( x \), which gives us \( x < 1 \). This means the domain consists of all real numbers less than 1, so the domain can be written as \( (-\infty, 1) \).
Understanding the domain allows us to know where the graph of the function will exist on the x-axis.
For this particular function, the inside of the logarithm, \( 1-x \), must be positive. Therefore, we set the inequality \( 1-x > 0 \) and solve for \( x \), which gives us \( x < 1 \). This means the domain consists of all real numbers less than 1, so the domain can be written as \( (-\infty, 1) \).
Understanding the domain allows us to know where the graph of the function will exist on the x-axis.
Natural Logarithm
The natural logarithm, represented by \( \ln(x) \), is a special type of logarithm where the base is the mathematical constant \( e \), approximately equal to 2.718. This logarithm is profound in mathematics because it naturally arises in many natural growth and decay processes.
The function \( y = -\ln(1-x) \) involves a natural logarithm with the "\( 1-x \)" adjustment. Let's break down why this matters:
The function \( y = -\ln(1-x) \) involves a natural logarithm with the "\( 1-x \)" adjustment. Let's break down why this matters:
- The negative sign in front of \( \ln(x) \) means the curve will be reflected over the x-axis, resulting in a downward slope.
- The shift from \( x \) to \( 1-x \) affects the domain and the positioning of the curve on the graph.
Asymptotes
An asymptote is a line that a graph approaches but never quite reaches. They can guide us in understanding the behavior of a function as it extends towards specific points in its domain or beyond.
For the function \( y = -\ln(1-x) \), as \( x \) approaches 1 from the left (\( x \to 1^- \)), the term \( 1-x \) approaches zero, causing \( \ln(1-x) \) to tend towards \( -\infty \). The negative in the function causes this to become \( \infty \), so \( y = -\ln(1-x) \to -\infty \).
This behavior results in a vertical asymptote at \( x = 1 \). This means the graph will decline sharply downward as it nears this line and provides insight into how the graph behaves as \( x \) increases within its domain toward 1.
Recognizing asymptotes is key in shaping the function's graph and understanding its limits.
For the function \( y = -\ln(1-x) \), as \( x \) approaches 1 from the left (\( x \to 1^- \)), the term \( 1-x \) approaches zero, causing \( \ln(1-x) \) to tend towards \( -\infty \). The negative in the function causes this to become \( \infty \), so \( y = -\ln(1-x) \to -\infty \).
This behavior results in a vertical asymptote at \( x = 1 \). This means the graph will decline sharply downward as it nears this line and provides insight into how the graph behaves as \( x \) increases within its domain toward 1.
Recognizing asymptotes is key in shaping the function's graph and understanding its limits.