Chapter 2: Problem 26
Find the domain and range of the function, and b) sketch a comprehensive graph of the function clearly indicating any intercepts or asymptotes. $$f: x \mapsto \frac{1}{x-5}$$
Short Answer
Expert verified
Domain: \((-\infty, 5) \cup (5, \infty)\); Range: \((-\infty, 0) \cup (0, \infty)\). Derive graph from the critical points and asymptotes.
Step by step solution
01
Identify the Domain
The domain of a function is the set of all possible input values (x-values) which will output a valid value from the function. For the function \( f(x) = \frac{1}{x-5} \), the denominator must not be zero because division by zero is undefined. Hence, we set \( x-5 eq 0 \), solving this gives \( x eq 5 \). Therefore, the domain of \( f \) is all real numbers except \( x = 5 \). Thus, the domain is \( (-\infty, 5) \cup (5, \infty) \).
02
Determine the Range
The range of a function is the set of all possible output values (y-values). For the function \( f(x) = \frac{1}{x-5} \), \( f(x) \) can approach any real number as \( x \) approaches 5 from either side, it approaches \( \infty \) or \(-\infty\), but \( f(x) \) will never be zero. Hence, the range is all real numbers except \( y = 0 \), which is \( (-\infty, 0) \cup (0, \infty) \).
03
Analyze Intercepts and Asymptotes
To find the y-intercept, set \( x = 0 \): \( f(0) = \frac{1}{0-5} = -\frac{1}{5} \). Thus, the y-intercept is \((0, -\frac{1}{5})\). There's no x-intercept because \( f(x) = 0 \) has no solutions (the numerator can never be zero). The vertical asymptote occurs where the function is undefined: \( x = 5 \). As \( x \rightarrow 5 \), \( f(x) \rightarrow \pm\infty \). The horizontal asymptote is \( y = 0 \) as \( x \rightarrow \pm\infty \), \( f(x) \rightarrow 0 \).
04
Sketch the Graph
Plot the vertical asymptote as a dashed line at \( x = 5 \) and the horizontal asymptote as a dashed line at \( y = 0 \). Plot the point \( (0, -\frac{1}{5}) \), which is the y-intercept. For \( x > 5 \), \( f(x) \rightarrow \infty \) as \( x \rightarrow 5^+ \) and \( f(x) \rightarrow 0^+ \) as \( x \rightarrow \infty \). For \( x < 5 \), \( f(x) \rightarrow -\infty \) as \( x \rightarrow 5^- \) and \( f(x) \rightarrow 0^- \) as \( x \rightarrow -\infty \). The graph is hyperbolic with two branches.
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Asymptotes
Asymptotes are lines that a graph approaches but never actually touches. In our case with the function \( f(x) = \frac{1}{x-5} \), we see both vertical and horizontal asymptotes.
Vertical asymptotes occur where the function is undefined. When you plug in \( x = 5 \), the function becomes undefined because the denominator equals zero. Thus, \( x = 5 \) is our vertical asymptote. It acts as a boundary the graph cannot cross, and as \( x \) gets infinitesimally close to 5, \( f(x) \) shoots off to positive or negative infinity.
Horizontal asymptotes give us behavior at the extremes as \( x \) approaches infinity. As \( x \) becomes extremely large or small, \( f(x) \) will get closer and closer to 0, making \( y = 0 \) the horizontal asymptote. This tells us the direction in which the branches of the hyperbola flatten out but never actually reach a y-value of zero.
Vertical asymptotes occur where the function is undefined. When you plug in \( x = 5 \), the function becomes undefined because the denominator equals zero. Thus, \( x = 5 \) is our vertical asymptote. It acts as a boundary the graph cannot cross, and as \( x \) gets infinitesimally close to 5, \( f(x) \) shoots off to positive or negative infinity.
Horizontal asymptotes give us behavior at the extremes as \( x \) approaches infinity. As \( x \) becomes extremely large or small, \( f(x) \) will get closer and closer to 0, making \( y = 0 \) the horizontal asymptote. This tells us the direction in which the branches of the hyperbola flatten out but never actually reach a y-value of zero.
Intercepts
Intercepts are points where the graph crosses the axes.
The y-intercept is found by setting \( x \) to 0, leading us to calculate \( f(0) = \frac{1}{-5} = -\frac{1}{5} \). This gives us the y-intercept at the point \((0, -\frac{1}{5})\), meaning the graph crosses the y-axis there. It's a peculiar point because often you'll see the graph hitting somewhere at a more standard axis location, but it reflects how every graph is unique in its own right.
The x-intercept is the point where \( f(x) \) equals zero. However, for this function, you will find there are no x-intercepts. An x-intercept would require the numerator, which is always 1 here, to be zero. Since 1 is never zero, our function never actually touches the x-axis, perfectly aligning with the horizontal asymptote.
The y-intercept is found by setting \( x \) to 0, leading us to calculate \( f(0) = \frac{1}{-5} = -\frac{1}{5} \). This gives us the y-intercept at the point \((0, -\frac{1}{5})\), meaning the graph crosses the y-axis there. It's a peculiar point because often you'll see the graph hitting somewhere at a more standard axis location, but it reflects how every graph is unique in its own right.
The x-intercept is the point where \( f(x) \) equals zero. However, for this function, you will find there are no x-intercepts. An x-intercept would require the numerator, which is always 1 here, to be zero. Since 1 is never zero, our function never actually touches the x-axis, perfectly aligning with the horizontal asymptote.
Functions
Functions map input values to output values following a specific rule. For our function \( f(x) = \frac{1}{x - 5} \), the relationship involves division by \( (x - 5) \).
Understanding a function's domain and range is key to grasping its behavior. The domain refers to all x-values making the function valid. Here, any real number except \( x = 5 \) is part of the domain. The exclusion stems from division by zero, which is undefined in mathematics.
The range, on the other hand, consists of all possible y-values. Since \( f(x) \) can approach any real number but gets infinitely large or small around \( x = 5 \) and never reaches zero, every real number is part of the range except \( y = 0 \). The study of this function lets us visualize how especially with undefined points the graph steers clear horizontally and vertically, creating those unique asymptotes.
Understanding a function's domain and range is key to grasping its behavior. The domain refers to all x-values making the function valid. Here, any real number except \( x = 5 \) is part of the domain. The exclusion stems from division by zero, which is undefined in mathematics.
The range, on the other hand, consists of all possible y-values. Since \( f(x) \) can approach any real number but gets infinitely large or small around \( x = 5 \) and never reaches zero, every real number is part of the range except \( y = 0 \). The study of this function lets us visualize how especially with undefined points the graph steers clear horizontally and vertically, creating those unique asymptotes.