Chapter 4: Problem 71
Make a hand-drawn graph. Be sure to label all the asymptotes. List the domain and the \(x\) -intercepts and the \(y\) -intercepts. Check your work using \(a\) graphing calculator. $$f(x)=\frac{x^{3}+1}{x}$$
Short Answer
Expert verified
Vertical asymptote at x=0. No y-intercept. x-intercept at -1. Domain: (-∞,0) ∪ (0,∞).
Step by step solution
01
- Identify the function
The function given is \( f(x) = \frac{x^3 + 1}{x} \). Let's rewrite it to simplify: \( f(x) = x^2 + \frac{1}{x} \).
02
- Find the asymptotes
To find the vertical asymptotes, set the denominator equal to zero: \( x = 0 \). There is no horizontal asymptote because the degree of the numerator is greater than the degree of the denominator. However, there is an oblique asymptote: divide \( x^3 + 1 \) by \( x \), which yields \( x^2 \). So, the oblique asymptote is \( y = x^2 \).
03
- Determine the intercepts
For the y-intercept, set \( x = 0 \). Because \( \frac{1}{0} \) is undefined, there is no y-intercept. For the x-intercepts, set the numerator equal to zero: \( x^3 + 1 = 0 \). This factors to \( (x+1)(x^2-x+1) = 0 \). Thus, the x-intercept is \( x = -1 \).
04
- Define the domain
The domain is all real numbers except where the function is undefined. Since \( x \) cannot be zero: \( \text{Domain} = (-\infty, 0) \cup (0, \infty) \).
05
- Draw the graph
Draw the graph of \( f(x) = x^2 + \frac{1}{x} \) by hand. Mark the vertical asymptote at \( x = 0 \) and the oblique asymptote along \( y = x^2 \). Label the x-intercept at \( (-1, 0) \).
06
- Verify with a graphing calculator
Use a graphing calculator to plot \( f(x) = x^2 + \frac{1}{x} \) and check that your hand-drawn graph matches the calculator's output. Ensure all asymptotes and intercepts match.
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
vertical asymptote
Understanding vertical asymptotes is crucial in precalculus graphing. A vertical asymptote occurs where the function approaches infinity as the input approaches a specific value. It happens where the denominator of a rational function equals zero, making the function undefined.
For the function given, \( f(x) = \frac{x^3 + 1}{x} \), the denominator is \( x \). Setting \( x \) to zero indicates the vertical asymptote at \( x = 0 \). Graphically, this means the function has a value approaching positive or negative infinity as \( x \) approaches zero from either side.
Always remember:
For the function given, \( f(x) = \frac{x^3 + 1}{x} \), the denominator is \( x \). Setting \( x \) to zero indicates the vertical asymptote at \( x = 0 \). Graphically, this means the function has a value approaching positive or negative infinity as \( x \) approaches zero from either side.
Always remember:
- Vertical asymptotes indicate undefined points.
- They're a key part of sketching rational functions.
oblique asymptote
An oblique asymptote, also known as a slant asymptote, appears when the degree of the polynomial in the numerator is exactly one greater than the degree of the polynomial in the denominator.
In our function \( f(x) = \frac{x^3 + 1}{x} \), the degree of the numerator (3) is one more than the degree of the denominator (1). To find the oblique asymptote, we perform polynomial division:
\[ \frac{x^3 + 1}{x} = x^2 + \frac{1}{x} \]
This yields \[ y = x^2 \], representing the oblique asymptote. This indicates that as \( x \) approaches positive or negative infinity, the function \( f(x) \) behaves like \( y = x^2 \).
Key points:
In our function \( f(x) = \frac{x^3 + 1}{x} \), the degree of the numerator (3) is one more than the degree of the denominator (1). To find the oblique asymptote, we perform polynomial division:
\[ \frac{x^3 + 1}{x} = x^2 + \frac{1}{x} \]
This yields \[ y = x^2 \], representing the oblique asymptote. This indicates that as \( x \) approaches positive or negative infinity, the function \( f(x) \) behaves like \( y = x^2 \).
Key points:
- Oblique asymptotes occur only with specific polynomials.
- They aid in understanding the end behavior of graphs.
domain and intercepts
Domains and intercepts provide valuable insight into the behavior of functions.
For the given function \( f(x) = \frac{x^3 + 1}{x}\), the domain excludes values that make the denominator zero. Therefore, the domain is:
\(\text{Domain} = (-\infty, 0) \cup (0, \infty) \)\br>
Intercepts are where the function crosses the axes:
For the given function \( f(x) = \frac{x^3 + 1}{x}\), the domain excludes values that make the denominator zero. Therefore, the domain is:
\(\text{Domain} = (-\infty, 0) \cup (0, \infty) \)\br>
Intercepts are where the function crosses the axes:
- Y-intercept: Set \( x = 0 \). But \( \frac{1}{0} \) is undefined, so there's no y-intercept.
- X-intercepts: Set the numerator to zero: \( x^3 + 1 = 0\). This factors to \((x + 1)(x^2 - x + 1) = 0 \), yielding \( x = -1 \) as the x-intercept.
- Domain indicates possible input values.
- X and y-intercepts show how functions cross the axes.
graphing calculator
Using a graphing calculator can verify hand-drawn graphs and help visualize functions more accurately.
Here are steps to use it for our function \( f(x) = x^2 + \frac{1}{x} \):
Here are steps to use it for our function \( f(x) = x^2 + \frac{1}{x} \):
- Enter the function: Input \( f(x) \) into the calculator.
- View the graph: Observe the plotted graph on the screen.
- Check asymptotes and intercepts: Confirm the vertical asymptote at \( x = 0 \), the oblique asymptote \( y = x^2 \), and the x-intercept at \( x = -1 \).
- Provides a visual aid for complex functions.
- Helps in verifying manual calculations.