# Infinite limits - vertical asymptotes

##### Intros
###### Lessons
1. Introduction to Vertical Asymptotes
2. finite limits VS. infinite limits
3. infinite limits translate to vertical asymptotes on the graph of a function
4. vertical asymptotes and curve sketching
##### Examples
###### Lessons
1. Determine Infinite Limits Graphically

For the function $f$ whose graph is shown, state the following:
1. $\lim_{x \to - {4^ - }} \;f\left( x \right)$
$\lim_{x \to - {4^ + }} \;f\left( x \right)$
$\lim_{x \to - 4} \;f\left( x \right)$
2. $\lim_{x \to {1^ - }} \;f\left( x \right)$
$\lim_{x \to {1^ + }} \;f\left( x \right)$
$\lim_{x \to 1} \;f\left( x \right)$
3. $\lim_{x \to {3^ - }} \;f\left( x \right)$
$\lim_{x \to {3^ + }} \;f\left( x \right)$
$\lim_{x \to 3} \;f\left( x \right)$
4. $\lim_{x \to {5^ - }} \;f\left( x \right)$
$\lim_{x \to {5^ + }} \;f\left( x \right)$
$\lim_{x \to 5} \;f\left( x \right)$
2. Evaluate Infinite Limits Algebraically
Find:
1. $\lim_{x \to {0^ - }} \;\frac{1}{x}$
$\lim_{x \to {0^ + }} \;\frac{1}{x}$
$\lim_{x \to 0} \;\frac{1}{x}$
2. $\lim_{x \to {0^ - }} \;\frac{1}{{{x^2}}}$
$\lim_{x \to {0^ + }} \;\frac{1}{{{x^2}}}$
$\lim_{x \to 0} \;\frac{1}{{{x^2}}}$
3. Evaluate Limits Algebraically
Find:
$\lim_{x \to {2^ - }} \;\frac{{5x}}{{x - 2}}$
$\lim_{x \to {2^ + }} \;\frac{{5x}}{{x - 2}}$
$\lim_{x \to 2} \;\frac{{5x}}{{x - 2}}$
1. Determine Infinite Limits of Log Functions
Determine:
$\lim_{x \to {0^ + }} \ln x$
###### Topic Notes
Limits don't always necessarily give numerical solutions. What happens if we take the limit of a function near its vertical asymptotes? We will answer this question in this section, as well as exploring the idea of infinite limits using one-sided limits and two-sided limits.

## Introduction

Infinite limits and vertical asymptotes are fundamental concepts in calculus that explore the behavior of functions as they approach certain values or points. This introduction video provides a comprehensive overview of these topics, laying the foundation for a deeper understanding of their applications and significance.

Infinite limits deal with the behavior of a function as its input approaches a specific value, often infinity or negative infinity. By analyzing the limit, we can determine how the function behaves in the vicinity of that value, even if the function is not defined at that point. Vertical asymptotes, on the other hand, are vertical lines that a function approaches but never crosses, indicating points where the function is undefined or exhibits infinite behavior.

This video serves as an essential starting point for students, educators, and anyone interested in mastering these concepts. It breaks down the intricacies of infinite limits and vertical asymptotes, providing clear explanations, illustrative examples, and practical applications. Whether you're a beginner or seeking to reinforce your knowledge, this introduction video offers a solid foundation for further exploration and understanding.

## Understanding Infinite Limits

In the realm of calculus, infinite limits arise when evaluating the behavior of functions as they approach certain values or points in their domain. These limits are encountered when a function encounters domain issues, such as vertical asymptotes or discontinuities, preventing it from being defined at specific points. Infinite limits are classified into two types: one-sided limits (left and right limits) and two-sided limits.

One-sided limits, also known as left and right limits, describe the behavior of a function as it approaches a specific point from either the left or right side of the domain. The left limit represents the limit as the input values approach the point from the left, while the right limit represents the limit as the input values approach the point from the right.

For example, consider the function f(x) = (x^2 - 1) / (x - 1). This function has a vertical asymptote at x = 1, where it is undefined. However, we can evaluate the one-sided limits to understand its behavior near this point. The left limit, lim(x1) f(x) = 2, indicates that as x approaches 1 from the left, the function approaches the value 2. Similarly, the right limit, lim(x1) f(x) = 2, indicates that as x approaches 1 from the right, the function also approaches the value 2.

Infinite limits occur when a function's value grows without bound as it approaches a specific point or value in its domain. These limits can be positive or negative infinity, denoted by + and -, respectively. Infinite limits often arise due to vertical asymptotes, where the function's graph approaches but never touches the vertical line.

For instance, consider the function g(x) = 1 / x. As x approaches 0 from the positive side, the function's values become increasingly large and approach positive infinity, represented as lim(x0) g(x) = +. Conversely, as x approaches 0 from the negative side, the function's values become increasingly negative and approach negative infinity, represented as lim(x0) g(x) = -.

Understanding infinite limits and one-sided limits is crucial in calculus, as they provide insights into the behavior of functions near critical points or regions where they are undefined. These concepts lay the foundation for advanced topics such as continuity, differentiation, and integration, and have numerous applications in various fields, including physics, engineering, and economics.

## Vertical Asymptotes and Their Graphical Significance

In the realm of graphical analysis, vertical asymptotes play a crucial role in understanding the behavior of functions. These asymptotes represent the values of the independent variable (x) where the function approaches positive or negative infinity. Graphically, vertical asymptotes manifest as vertical lines on the graph, indicating regions where the function's values become unbounded or approach infinity.

The concept of infinite limits is closely tied to vertical asymptotes. When the limit of a function approaches positive or negative infinity as the input variable approaches a certain value, it signifies the presence of a vertical asymptote on the graph. These asymptotes act as boundaries that the graph cannot cross, resulting in distinct behaviors on either side of the asymptote.

To illustrate the graphical significance of vertical asymptotes, let's consider the following examples:

1. Positive Vertical Asymptote:

Consider the function f(x) = 1 / (x - 2). As x approaches 2 from either side, the function's values approach positive infinity. Graphically, this translates to a vertical asymptote at x = 2, where the graph approaches the vertical line from both sides but never touches or crosses it. The graph exhibits a distinct behavior on either side of the asymptote, with the function values increasing rapidly as x approaches 2 from the left and decreasing rapidly as x approaches 2 from the right.

For the function g(x) = -1 / (x + 3), as x approaches -3 from either side, the function's values approach negative infinity. This results in a negative vertical asymptote at x = -3, where the graph approaches the vertical line from both sides but never intersects it. The graph's behavior is characterized by the function values decreasing rapidly as x approaches -3 from the left and increasing rapidly as x approaches -3 from the right.

The presence of vertical asymptotes significantly impacts the graph's behavior and shape. On one side of the asymptote, the graph may exhibit a particular trend, while on the other side, it may display a completely different behavior. This abrupt change in the graph's trajectory is a direct consequence of the function's values approaching infinity at the asymptote.

It's important to note that vertical asymptotes can occur at multiple points on the graph, leading to different regions of behavior separated by these asymptotes. Additionally, some functions may have both positive and negative vertical asymptotes, further complicating the graph's shape and behavior.

In summary, vertical asymptotes play a crucial role in graphical analysis by representing the values of the independent variable where the function approaches positive or negative infinity. These asymptotes act as boundaries that the graph cannot cross, resulting in distinct behaviors on either side. Understanding the graphical significance of vertical asymptotes is essential for interpreting and analyzing the behavior of functions in various mathematical and scientific contexts.

## Techniques for Evaluating Infinite Limits

Evaluating infinite limits is a crucial concept in calculus and mathematical analysis, as it helps us understand the behavior of functions as they approach infinity. There are various techniques that can be employed to evaluate infinite limits, including numerical analysis and algebraic methods.

Numerical analysis involves using computational methods to approximate the value of a limit as the input approaches a specific value. This technique is particularly useful when dealing with complex functions or when algebraic methods become cumbersome. One common numerical approach is the use of iterative algorithms, such as the Newton-Raphson method, which can converge to the desired limit with increasing precision.

Algebraic methods, on the other hand, involve manipulating the algebraic expression of the function to determine its behavior as it approaches infinity. These methods often rely on algebraic techniques such as factoring, rationalizing, and applying various limit laws and theorems. For example, the limit of a rational function can be evaluated by factoring the numerator and denominator and applying the appropriate rules for limits involving polynomials and rational expressions.

When evaluating infinite limits, it is crucial to determine whether the limit approaches positive or negative infinity. This can be done by analyzing the behavior of the function near the vertical asymptote, which is the point where the function approaches infinity. If the function approaches positive values as it gets closer to the asymptote from the left, the limit is said to approach positive infinity. Conversely, if the function approaches negative values as it gets closer to the asymptote from the right, the limit is said to approach negative infinity.

To illustrate this concept, consider the function f(x) = (x^2 - 1) / (x - 1). As x approaches 1 from the left, the numerator becomes increasingly negative, while the denominator approaches 0. Therefore, the limit of f(x) as x approaches 1 from the left is negative infinity. On the other hand, as x approaches 1 from the right, the numerator becomes increasingly positive, while the denominator approaches 0. Consequently, the limit of f(x) as x approaches 1 from the right is positive infinity.

## Curve Sketching and Rational Functions

Curve sketching is a fundamental technique in calculus that involves graphing functions by analyzing their behavior and characteristics. When it comes to rational functions, which are quotients of two polynomial functions, curve sketching becomes particularly important due to the presence of vertical asymptotes and potential domain restrictions.

A rational function is defined as f(x) = P(x) / Q(x), where P(x) and Q(x) are polynomial functions. The domain of a rational function is the set of all x values for which the denominator Q(x) is non-zero. This is because division by zero is undefined. Consequently, the x values that make the denominator zero are excluded from the domain, leading to domain restrictions.

One of the key aspects of sketching rational function graphs is identifying vertical asymptotes. A vertical asymptote occurs when the denominator Q(x) is equal to zero, and the numerator P(x) is non-zero. At these points, the graph of the rational function approaches positive or negative infinity, creating a vertical asymptote. Identifying these asymptotes is crucial for understanding the overall shape and behavior of the graph.

Another important consideration when sketching rational function graphs is the presence of holes. Holes occur when both the numerator P(x) and the denominator Q(x) are equal to zero for the same x value. At these points, the function is undefined, and the graph will have a hole or a missing point.

To sketch a rational function graph, follow these steps:

1. Find the domain of the function by setting the denominator Q(x) not equal to zero and solving for x.
2. Identify the vertical asymptotes by setting the denominator Q(x) equal to zero and solving for x.
3. Find the x-intercepts by setting the numerator P(x) equal to zero and solving for x.
4. Determine the behavior of the graph as x approaches positive and negative infinity by examining the highest degree terms in the numerator and denominator.
5. Plot the x-intercepts, vertical asymptotes, and any holes or other critical points.
6. Sketch the graph by considering the behavior near the asymptotes, holes, and other critical points, as well as the overall shape determined by the degree of the numerator and denominator.

For example, consider the rational function f(x) = (x^2 - 4) / (x^2 - 9). The domain of this function is all real numbers except x = ±3, since the denominator is zero at those points. The vertical asymptotes occur at x = ±3. The x-intercepts are at x = ±2, where the numerator is zero. The graph will have a hole at the origin (0, 0) since both the numerator and denominator are zero at x = 0. The asymptotic behavior shows that the graph approaches positive infinity as x approaches positive infinity, and negative infinity as x approaches negative infinity.

By carefully analyzing the domain restrictions, vertical asymptotes, holes, and asymptotic behavior, you can accurately sketch the graph of a rational function, providing a visual representation of its behavior and characteristics.

## Conclusion

In this outline, we explored the concept of infinite limits and their graphical representation through vertical asymptotes. Understanding infinite limits is crucial in calculus and real-world applications, as it helps us analyze the behavior of functions as they approach certain values. The introduction video provided a solid foundation for grasping these concepts, and we encourage you to revisit it if needed. Additionally, we recommend exploring the further resources available to deepen your understanding and gain more practice with infinite limits and asymptotes. Mastering these topics will not only enhance your mathematical skills but also prepare you for more advanced concepts in calculus and related fields.

### Example:

Determine Infinite Limits Graphically

For the function $f$ whose graph is shown, state the following:
$\lim_{x \to - {4^ - }} \;f\left( x \right)$
$\lim_{x \to - {4^ + }} \;f\left( x \right)$
$\lim_{x \to - 4} \;f\left( x \right)$

#### Step 1: Understanding the Problem

In this question, we are tasked with finding the limit of a function from the graph provided. The limits we need to determine are as $x$ approaches -4 from the left, from the right, and from both directions. This involves understanding the behavior of the function near the point $x = -4$.

#### Step 2: Finding the Left-Hand Limit

First, we need to find the limit of the function as $x$ approaches -4 from the left, denoted as $\lim_{x \to -4^-} f(x)$. To do this, observe the graph as $x$ gets closer to -4 from values less than -4. Notice how the function behaves as it approaches this point. From the graph, we can see that as $x$ approaches -4 from the left, the value of the function increases without bound in the positive direction. Therefore, the left-hand limit is positive infinity.

#### Step 3: Identifying Vertical Asymptotes

Whenever we encounter an infinite limit as $x$ approaches a certain number, it indicates the presence of a vertical asymptote at that number. In this case, since the limit as $x$ approaches -4 from the left is positive infinity, we should expect a vertical asymptote at $x = -4$. This means the function has a vertical line at $x = -4$ where the function values increase without bound.

#### Step 4: Finding the Right-Hand Limit

Next, we need to find the limit of the function as $x$ approaches -4 from the right, denoted as $\lim_{x \to -4^+} f(x)$. To do this, observe the graph as $x$ gets closer to -4 from values greater than -4. From the graph, we can see that as $x$ approaches -4 from the right, the value of the function also increases without bound in the positive direction. Therefore, the right-hand limit is positive infinity.

#### Step 5: Determining the Two-Sided Limit

Finally, we need to find the limit of the function as $x$ approaches -4 from both directions, denoted as $\lim_{x \to -4} f(x)$. If the direction is not specified, we must consider approaching the number from both the left and the right. The two-sided limit exists only if the left-hand limit is equal to the right-hand limit. In this case, both the left-hand limit and the right-hand limit are positive infinity. Therefore, the two-sided limit exists and is equal to positive infinity.

### FAQs

1. What is the difference between one-sided limits and two-sided limits?

One-sided limits, also known as left and right limits, describe the behavior of a function as it approaches a specific point from either the left or right side of the domain. The left limit represents the limit as the input values approach the point from the left, while the right limit represents the limit as the input values approach the point from the right. Two-sided limits, on the other hand, consider the behavior of the function as it approaches the point from both sides simultaneously.

2. How do vertical asymptotes relate to infinite limits?

Vertical asymptotes and infinite limits are closely related concepts. A vertical asymptote occurs when a function approaches positive or negative infinity as the input variable approaches a certain value. This behavior is represented by an infinite limit, where the function's values become unbounded or approach infinity at that point. Graphically, vertical asymptotes manifest as vertical lines on the graph, indicating regions where the function's values become infinite.

3. What are the techniques for evaluating infinite limits?

There are two main techniques for evaluating infinite limits: numerical analysis and algebraic methods. Numerical analysis involves using computational methods to approximate the value of a limit as the input approaches a specific value, while algebraic methods involve manipulating the algebraic expression of the function to determine its behavior as it approaches infinity. Algebraic methods often rely on techniques such as factoring, rationalizing, and applying various limit laws and theorems.

4. What is the significance of curve sketching for rational functions?

Curve sketching is particularly important for rational functions due to the presence of vertical asymptotes and potential domain restrictions. Identifying vertical asymptotes, holes, and asymptotic behavior is crucial for understanding the overall shape and behavior of the graph. Curve sketching for rational functions involves finding the domain, identifying vertical asymptotes, locating x-intercepts, and determining the asymptotic behavior as x approaches positive and negative infinity.

5. How do you determine the presence of a vertical asymptote in a rational function?

A vertical asymptote occurs in a rational function when the denominator is equal to zero, and the numerator is non-zero. To determine the presence of a vertical asymptote, you need to set the denominator equal to zero and solve for x. The resulting x values represent the locations of the vertical asymptotes.

### Prerequisite Topics

Understanding the concept of "Infinite limits - vertical asymptotes" requires a solid foundation in several prerequisite topics. Mastering polynomial functions is crucial because vertical asymptotes often arise from rational functions, which are formed by dividing polynomials. Additionally, rational functions play a significant role in determining the behavior of functions near vertical asymptotes.

Curve sketching techniques are essential for visualizing the behavior of functions, including their asymptotic behavior. By understanding how to sketch curves, students can better grasp the concept of vertical asymptotes and their impact on the graph of a function. Furthermore, limit laws provide the mathematical tools necessary to evaluate limits and determine the existence of vertical asymptotes.

Mastering these prerequisite topics will not only enhance your understanding of infinite limits and vertical asymptotes but also lay a solid foundation for more advanced calculus concepts. By building a strong grasp of polynomial functions, rational functions, curve sketching, and limit laws, you will be better equipped to tackle the intricacies of vertical asymptotes and their implications in calculus and beyond.

i)
${\;}\lim_{x \to {a^ - }} f\left( x \right) =\infty$
ii)
$\lim_{x \to {a^ + }} f\left( x \right) =\infty$
iii)
$\lim_{x \to {a^ - }} f\left( x \right) =,- \infty$
iv)
$\lim_{x \to {a^ + }} f\left( x \right) =,- \infty$