Chapter 2: Problem 53
Find the limits in Exercises \(53-58.\) $$\lim \frac{1}{x^{2}-4}\text{ as }$$ \begin{equation}\begin{array}{ll}{\text { a. }} & {x \rightarrow 2^{+}} & {\text { b. } x \rightarrow 2^{-}} \\ {\text { c. }} & {x \rightarrow-2^{+}} & {\text { d. } x \rightarrow-2^{-}}\end{array}\end{equation}
Short Answer
Expert verified
(a) +∞, (b) -∞, (c) -∞, (d) +∞.
Step by step solution
01
Identify the Function
The function given is \( f(x) = \frac{1}{x^2 - 4} \). Our goal is to determine the limit of \( f(x) \) as \( x \) approaches specific values. This will require us to consider the behavior of the denominator \( x^2 - 4 \) as \( x \) approaches each value.
02
Analyze Asymptotic Behavior for x Approaching from the Right (Positive)
Let's start with \( a. \) when \( x \rightarrow 2^{+} \). As \( x \) approaches 2 from the right, \( x = 2^+ \), the expression \( x^2 - 4 \) becomes a very small positive number because \( x^2 \) is slightly more than 4. Hence, \( \frac{1}{x^2 - 4} \) tends towards positive infinity. Thus, \[ \lim_{{x \to 2^{+}}} \frac{1}{x^2 - 4} = +\infty \]
03
Analyze Asymptotic Behavior for x Approaching from the Left (Negative)
Now for \( b. \), when \( x \rightarrow 2^{-} \). As \( x \) approaches 2 from the left, \( x = 2^- \), \( x^2 - 4 \) becomes a very small negative number, since \( x^2 \) is slightly less than 4. Hence, \( \frac{1}{x^2 - 4} \) tends towards negative infinity. \[ \lim_{{x \to 2^{-}}} \frac{1}{x^2 - 4} = -\infty \]
04
Analyze Asymptotic Behavior for x Approaching from the Right at Negative Value
Consider \( c. \) when \( x \rightarrow -2^{+} \). As \( x \) approaches -2 from the right, \( x = -2^+ \), we find that \( x^2 - 4 \) becomes a small negative number because \( x^2 \) is close to 4 but less than it. Therefore, \( \frac{1}{x^2 - 4} \) will tend towards negative infinity. \[ \lim_{{x \to -2^{+}}} \frac{1}{x^2 - 4} = -\infty \]
05
Analyze Asymptotic Behavior for x Approaching from the Left at Negative Value
Finally, for \( d. \) where \( x \rightarrow -2^{-} \). As \( x \) approaches -2 from the left, \( x = -2^- \), \( x^2 - 4 \) becomes a small positive number since \( x^2 \) is slightly more than 4. Consequently, \( \frac{1}{x^2 - 4} \) tends to positive infinity. \[ \lim_{{x \to -2^{-}}} \frac{1}{x^2 - 4} = +\infty \]
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Limits
In calculus, the limit of a function describes the behavior of the function's output as the input approaches a certain value. Limits are vital for understanding how functions behave near specific points, even if they do not reach those points. For example, when approaching 2 from either side in the function \( f(x) = \frac{1}{x^2 - 4} \), the output behavior becomes noticeable. If we consider the function as \( x \to 2^{+} \), the denominator becomes a very tiny positive value, making the fraction approach positive infinity. On the other hand, as \( x \to 2^{-} \), the denominator is a tiny negative value, which makes the fraction approach negative infinity.
- Limits help identify whether a function approaches a specific finite value or diverges to infinity.
- They indicate if the function possesses continuity near the point of interest.
- The behavior of the limit varies based on the direction of approach (right or left).
Asymptotic Behavior
Asymptotic behavior explains how a function behaves as it approaches a point or extends to infinity. In the context of the function \( f(x) = \frac{1}{x^2 - 4} \), it is crucial to examine as \( x \) gets close to values like 2 or -2. This function has vertical asymptotes at \( x = 2 \) and \( x = -2 \), where the denominator equals zero, causing the function to diverge to either positive or negative infinity.
- Vertical asymptotes indicate that the function's value grows indefinitely as it approaches a given \( x \) value.
- The behavior is determined by examining the numerator and the sign of the denominator as \( x \) approaches the asymptote.
- Understanding asymptotic behavior is essential in graphing functions and evaluating infinite limits.
One-Sided Limits
One-sided limits focus on the behavior of a function as it approaches a specific point from one direction: the left or the right. It allows a finer analysis when a function behaves differently on either side of a point. For instance, in \( f(x) = \frac{1}{x^2 - 4} \) as \( x \) approaches 2, the limit from the right, \( x \rightarrow 2^{+} \), diverges to positive infinity, while the limit from the left, \( x \rightarrow 2^{-} \), diverges to negative infinity.
- One-sided limits are noted with the superscripts \( + \) (from right) or \( - \) (from left).
- These limits provide insight into the slope and directionality of a graph at specific points.
- They are crucial for determining the presence of a jump or other discontinuity in a graph.