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In Exercises 5 and \(6,\) explain why the limits do not exist. $$\lim _{x \rightarrow 1} \frac{1}{x-1}$$

Short Answer

Expert verified
The limits from the left and right are not equal; hence, the limit does not exist.

Step by step solution

01

Understand the Limit

We are asked to find the limit \( \lim _{x \rightarrow 1} \frac{1}{x-1} \). This involves evaluating the behavior of the function \( \frac{1}{x-1} \) as \( x \) approaches 1.
02

Analyze Approach from the Left Side

Consider approaching \( x = 1 \) from the left, i.e., values of \( x \) close to 1 but less than 1. For such \( x \), \( x-1 \) is negative, thus \( \frac{1}{x-1} \) becomes a large negative number. As \( x \rightarrow 1^- \), \( \frac{1}{x-1} \rightarrow -\infty \).
03

Analyze Approach from the Right Side

Now consider approaching \( x = 1 \) from the right, i.e., values of \( x \) greater than 1. For such \( x \), \( x-1 \) is positive, and \( \frac{1}{x-1} \) becomes a large positive number. As \( x \rightarrow 1^+ \), \( \frac{1}{x-1} \rightarrow \infty \).
04

Conclude the Non-existence of the Limit

Notice that approaching 1 from the left (\( x \rightarrow 1^- \)) results in \( -\infty \) while approaching from the right (\( x \rightarrow 1^+ \)) results in \( \infty \). Because the left-hand limit and the right-hand limit are not equal, the limit \( \lim _{x \rightarrow 1} \frac{1}{x-1} \) does not exist.

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

One-Sided Limits
One-sided limits explore what happens to a function as the variable approaches a specific value from one direction.
In limit problems, this means evaluating the behavior of the function as you approach the target value from either the left or the right.
  • **Left-Hand Limit:** Denoted as \(x \to a^-\), this examines what happens as \(x\) approaches \(a\) from values less than \(a\). If \(f(x)\) approaches a finite number, then the left-hand limit exists and equals that number.
  • **Right-Hand Limit:** Denoted as \(x \to a^+\), this looks at what happens as \(x\) approaches \(a\) from values greater than \(a\). If \(f(x)\) approaches a finite number, then the right-hand limit exists and equals that number.
For the function \(\frac{1}{x-1}\), analyzing the one-sided limits at \(x = 1\) reveals different behaviors.
Approaching from the left, \(x \to 1^-\), the function takes on increasingly negative values, heading toward \(-\infty\).
From the right, \(x \to 1^+\), the function becomes positive and approaches \(\infty\).
These differing results from each side contribute to a limit that does not agree.
Infinite Limits
Infinite limits occur when the values of a function grow indefinitely large as the variable approaches a particular point.
Understanding this behavior is crucial to analyzing how functions behave at points that might lead to astronomical values.
  • **Positive Infinity:** This happens when as \(x\) approaches a particular point, \(f(x)\) increases without bound, denoted as \(\lim_{x \to a} f(x) = \infty\).
  • **Negative Infinity:** Conversely, if \(f(x)\) decreases without bound as \(x\) approaches a point, it is described as \(\lim_{x \to a} f(x) = -\infty\).
The function \(\frac{1}{x-1}\) illustrates both infinite behaviors as \(x\) approaches 1.
Approaching from the left, it exhibits a negative infinite limit, \(-\infty\), and from the right, a positive infinite limit, \(\infty\).
These infinite limits help explain why the overall limit does not exist.
Limit Does Not Exist
In calculus, sometimes calculating the limit results in a situation where it simply does not exist.
This typically happens when one or more of the following occur:
  • **Disparity Between One-Sided Limits:** If the left-hand and right-hand limits are unequal, as in \(\lim_{x \to 1^-} \frac{1}{x-1} = -\infty\) and \(\lim_{x \to 1^+} \frac{1}{x-1} = \infty\), the limit doesn't exist.
  • **Unbounded Growth:** If the function approaches infinity (positive or negative) as it nears a specific \(x\)-value, like in our example, the limit can be said to not exist.
  • **Oscillation:** Sometimes, functions oscillate wildly within a limited interval and thus evade settling into any single value.
In our given function example, \(\frac{1}{x-1}\), the one-sided limits both approach infinity, demonstrating that the function is unbounded as \(x\) becomes 1.
Without a single, agreed-upon endpoint, the limit \(\lim _{x \rightarrow 1} \frac{1}{x-1}\) must indeed be accounted as nonexistent.

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