Chapter 2: Problem 29
Location of vertical asymptotes Analyze the following limits and find the vertical asymptotes of \(f(x)=\frac{x-5}{x^{2}-25}.\) \(\begin{array}{llll}\text { a. } \lim _{x \rightarrow 5} f(x) & \text { b. } \lim _{x \rightarrow-5^{-}} f(x) & \text { c. } \lim _{x \rightarrow-5^{+}} f(x)\end{array}\)
Short Answer
Expert verified
Answer: The vertical asymptote of the function is at \(x=-5\).
Step by step solution
01
Simplify the function
Firstly, we need to simplify the function. The denominator has a difference of squares which can be factored as \((x-5)(x+5)\), resulting in:
\(f(x) = \frac{x-5}{(x-5)(x+5)}\)
Now, we can cancel out the common factor \((x-5)\) from the numerator and the denominator:
\(f(x) = \frac{1}{x+5}\) for \(x \neq 5\)
It must be noted that the original function has a hole at \(x=5\), but it is not an asymptote, as the function is continuous at \(x=5\).
02
Determine the points where the denominator goes to 0
Now, we need to determine when the denominator of the simplified function goes to 0:
\(x+5=0 \Rightarrow x=-5\)
This shows that there is a vertical asymptote at \(x=-5\).
03
Analyze the limits for x approaching -5
Now, we need to analyze the limits given in the exercise for both left and right of the vertical asymptote at x=-5:
a. \(\lim_{x \rightarrow 5} f(x)\)
Since there is no vertical asymptote at x=5, as we already found it was a hole, we can simply evaluate the limit by plugging 5 into the simplified function:
\(\lim_{x \rightarrow 5} \frac{1}{x+5} = \frac{1}{5+5} = \frac{1}{10}\)
b. \(\lim_{ x \rightarrow -5^{-} } f(x)\)
In this case, we are approaching -5 from the left. Let's plug in the simplified function:
\(\lim_{ x \rightarrow -5^{-} } \frac{1}{x+5}\)
As x approaches -5 from the left, the denominator goes to 0, and we have \(\frac{1}{-}(a small number)\), so the limit is \(-\infty\).
c. \(\lim_{ x \rightarrow -5^{+} } f(x)\)
Similarly, we are approaching -5 from the right:
\(\lim_{ x \rightarrow -5^{+} } \frac{1}{x+5}\)
As x approaches -5 from the right, the denominator goes to 0, but this time we have \(\frac{1}{+}(a tiny number)\), so the limit is \(+\infty\).
04
Conclusion
From our analysis, we have concluded the following:
a. \(\lim_{x \rightarrow 5} f(x) = \frac{1}{10}\)
b. \(\lim_{ x \rightarrow -5^{-} } f(x) = -\infty\)
c. \(\lim_{ x \rightarrow -5^{+} } f(x) = +\infty\)
The function \(f(x)=\frac{x-5}{x^{2}-25}\) has a vertical asymptote at \(x=-5\) since the limits approach infinity on both sides, confirming the singularity.
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Limits
In calculus, a **limit** is a fundamental concept that describes the behavior of a function as its input approaches a particular value. To understand this idea, imagine approaching a destination point on a road. As you get nearer, the limit tells you what the road does—whether it continues smoothly, ends, or takes a sharp turn.
With the function \(f(x)=\frac{x-5}{x^2-25}\), we analyzed the behavior as \(x\) approached certain values to find the limits. For instance:
With the function \(f(x)=\frac{x-5}{x^2-25}\), we analyzed the behavior as \(x\) approached certain values to find the limits. For instance:
- As \(x\) moves towards 5, the function remains smooth, simplifying to \(\frac{1}{10}\), indicating continuity rather than a vertical asymptote—only a removable discontinuity or a 'hole'.
- In contrast, approaching \(-5\) from the left or right, the function behaves differently, with limits heading towards \(-\infty\) or \(+\infty\) respectively.
Rational Functions
**Rational functions** are expressions of the form \(\frac{P(x)}{Q(x)}\), where both \(P(x)\) and \(Q(x)\) are polynomials. These functions can exhibit a variety of behaviors, including continuity, points of discontinuity, and asymptotes.
In the example provided, \(f(x) = \frac{x-5}{x^2-25}\) is broken down into simpler factors by recognizing the denominator as a difference of squares: \((x-5)(x+5)\).
In the example provided, \(f(x) = \frac{x-5}{x^2-25}\) is broken down into simpler factors by recognizing the denominator as a difference of squares: \((x-5)(x+5)\).
- After canceling common factors in the numerator and the denominator, the original representation highlights that \(x=5\) leads to a removable discontinuity (a hole), not an asymptote.
- Recognizing this factorization enables us to understand the function better by identifying potential points for vertical asymptotes, such as \(x=-5\) where the denominator equals zero.
Asymptotic Behavior
**Asymptotic behavior** in mathematics describes how functions behave as they move towards infinitely large or small values. This notion is particularly important in understanding vertical asymptotes, where a function tends to increase or decrease indefinitely as it approaches a certain value of \(x\).
With the given function \(f(x)=\frac{x-5}{x^2-25}\), studying its asymptotic behavior involves recognizing where the function dramatically spikes towards positive or negative infinity:
With the given function \(f(x)=\frac{x-5}{x^2-25}\), studying its asymptotic behavior involves recognizing where the function dramatically spikes towards positive or negative infinity:
- For \(x\rightarrow -5\), the reduced function \(f(x) = \frac{1}{x+5}\) heads rapidly towards infinity, highlighting a vertical asymptote at \(x=-5\).
- As \(x\) approaches this asymptote from the left, the function dips accordingly to \(-\infty\), while from the right, it rises to \(+\infty\).