Chapter 4: Problem 27
Sketch the graph of \(f\). $$ f(x)=\frac{-2 x^{2}+10 x-12}{x^{2}+x} $$
Short Answer
Expert verified
The graph has vertical asymptotes at \( x=0 \), \( x=-1 \), a horizontal asymptote at \( y=-2 \), and x-intercepts at \( x=3 \), and \( x=2 \).
Step by step solution
01
Determine the Domain
To find the domain of the function \( f(x) = \frac{-2x^2 + 10x - 12}{x^2 + x} \), set the denominator equal to zero and solve for \( x \). The denominator is \( x^2 + x = 0 \), which factors as \( x(x+1) = 0 \). Therefore, the domain is all real numbers except \( x = 0 \) and \( x = -1 \).
02
Find the Asymptotes
For vertical asymptotes, set the denominator \( x^2 + x = 0 \). Thus, vertical asymptotes are at \( x = 0 \) and \( x = -1 \). For horizontal asymptotes, compare the degree of the numerator \(-2x^2 + 10x - 12\) and the denominator \(x^2 + x\). Since they are the same, the horizontal asymptote is at \( y = \frac{-2}{1} = -2 \).
03
Determine Intercepts
To find the y-intercept, evaluate \( f(0) \), but this leads to division by zero, so no y-intercept exists. Find x-intercepts by setting the numerator \(-2x^2 + 10x - 12 = 0\). Factoring gives \(-2(x-3)(x-2) = 0\). The x-intercepts are \( x = 3 \) and \( x = 2 \).
04
Analyze Behavior Between Asymptotes and Intercepts
Check the behavior of the function around the asymptotes \( x = 0 \) and \( x = -1 \), as well as intervals between the intercepts. For example, check sample points to determine whether \( f(x) \) approaches \( \pm \infty \) or follows the asymptote (\( y= -2 \)).
05
Sketch the Graph
Combine all gathered information: domain, intercepts, asymptotes, and behavior analysis. Draw the vertical asymptotes as dashed lines at \( x = 0 \) and \( x = -1 \), the horizontal line at \( y = -2 \), and plot the intercepts at \( (3,0) \) and \( (2,0) \). Sketch the curve approaching asymptotes and passing through intercepts.
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Domain of Rational Functions
The domain of rational functions refers to all possible x-values that a function can take without leading to mathematically undefined situations. Specifically, for a function \[ f(x) = \frac{P(x)}{Q(x)} \]we need to determine when the denominator, \( Q(x) \), is not equal to zero. This is because division by zero is undefined. In our exercise, the denominator is \( x^2 + x \). **Steps to find the domain:**
- Factor the denominator: \( x(x + 1) = 0 \).
- Solve the equation: \( x = 0 \) and \( x = -1 \). These values make the denominator zero, hence they are excluded from the domain.
Asymptotes
Asymptotes are lines that the graph of a function approaches but never actually touches or crosses. For rational functions, these are typically vertical or horizontal. To locate them, we use:**Vertical Asymptotes:**- Vertical asymptotes occur where the denominator is zero, as long as the numerator is not zero at these points too. From our factorization:
- Vertical asymptotes are at \( x = 0 \) and \( x = -1 \).
- The horizontal asymptote is the ratio of the leading coefficients. Our function has a horizontal asymptote at \( y = -2 \), because the leading coefficients of the numerator and denominator are \(-2\) and \(1\), respectively.
Intercepts of Rational Functions
Intercepts are points where the graph of the function crosses the axes:**X-Intercepts:**- To find the x-intercepts, set the numerator equal to zero and solve for \( x \):
- \(-2x^2 + 10x - 12 = 0\). Factoring gives \(-2(x-3)(x-2) = 0\).
- The x-intercepts are \( x = 3 \) and \( x = 2 \).
Behavior Analysis of Graphs
Understanding the behavior of a graph involves examining how it behaves towards infinity and near asymptotes. This involves:**Analyzing Behavior Near Asymptotes:**- As we approach the vertical asymptotes at \( x = 0 \) and \( x = -1 \), the function can either head towards \( \infty \) or \(-\infty \). Evaluating points around these asymptotes helps determine the direction.**Behavior Between Intercepts:**- Check sample points in intervals divided by intercepts \( x = 2 \) and \( x = 3 \) to see if they lie above or below the horizontal asymptote \( y = -2 \).Such analysis gives insight into how the graph moves across its domain, whether it follows expected trends, and how it behaves near critical points like intercepts and asymptotes.