# Continuity

## Understanding Continuity in Functions

In the realm of mathematics, continuity in functions is a fundamental concept to comprehend, particularly when studying calculus. It refers to the smoothness and unbrokenness of a function at a specific point. In this article, we will dive into the intuitive understanding of continuity and its formal definition, as well as how to check for continuity at a given point.

### Intuitive Understanding of Continuity

To better grasp the concept of continuity, it may be helpful to think of it as "drawing a function without lifting your pencil." In other words, there should be no gaps or breaks in the function's graph. Let's explore this further by examining a single point, p.

Firstly, we must establish that the function is indeed defined at p. If it is not, we cannot draw it without interrupting the line, hence the phrase "assume exists." Additionally, the limits from the left and right of p must be equal for the function to be continuous at p. If they are unequal, the function is not continuous at that point.

Therefore, it is not enough for a function to have a value at p and equal limits from the left and right. It must also have the same limit as its function value. Let's now formalize this understanding into a definition.

### Defining Continuity

A function is continuous at p if and only if the following three conditions are met: **1.** exists, **2.** both limits from the left and right are equal, and **3.** the function value is equal to the limit. If any of these conditions are not fulfilled, the function is considered discontinuous at p.

The phrase "if and only if" represents a logical statement, indicating that both sides must be true for the statement to hold.

### Steps for Checking Continuity

To determine if a function is continuous at a particular point, we can follow these simple steps:

- Step 1: Verify that the function is defined at the given point. If not, the function is not continuous at that point.
- Step 2: Examine if exists. If not, the function is not continuous at that point.
- Step 3: Compare the limit and function value at the given point. If they are not equal, the function is not continuous at that point.

Note that some may use the term "discontinuity" to describe a function that does not exhibit continuity, but they convey the same meaning.

### Examples of Continuous Functions

Let's explore some examples to solidify our understanding of continuity.

**Example 1: Is the function continuous at ?**

If we try to evaluate the function at x=2, we encounter division by zero, indicating that the function is undefined at this point. Therefore, the function is not continuous at x=2. This can also be observed in the graph, where a vertical asymptote at x=2 signifies a discontinuity.

**Example 2: Is the function continuous at ?**

In this case, the function is defined at x=2, but the limit from the left and right either do not exist or are not equal. Hence, the function is not continuous at x=2, despite having a defined value at that point.

**Example 3: Is the function continuous at ?**

If we slightly alter the function, we can observe its effect on continuity. In this case, the limit as x approaches 2 is not infinity, rendering the function not continuous at x=2.

**Example 4: Is the function continuous at ?**

The key here is to pay attention to the question's context. Although the function's definition changes at x=2, the question pertains to continuity at x=3. In this scenario, the function is discontinuous at x=3, as the two definitions do not seamlessly merge at that point.

## The Concept of Continuity in Calculus

In calculus, the concept of continuity refers to the smoothness and connectedness of a function. Let's take a look at an example to understand continuity at a point.

Consider the function **f(x) = 2x + 3** and let's determine if it is continuous at the point **x = 2**.

**Step 1:**The function is defined at x = 2, as we can substitute 2 for x and get an output of 7.**Step 2:**When we approach x = 2 from the left, the limit is 2, and from the right, it is also 2. Therefore, the limits from both sides are equal.**Step 3:**The function value at x = 2 is also 7, hence the function value and the limit value align.

As all three conditions are met, we can conclude that the function **f(x) = 2x + 3** is continuous at x = 2.

## Another Illustration of Continuity

Let's consider another example with a slightly different function: **f(x) = 5x + 2** and point **x = 3**.

**Step 1:**The function is defined at x = 3, as we can substitute 3 for x and get an output of 17.**Step 2:**When we approach x = 3 from the left, the limit is 13, while from the right, it is 17. Since these two values are not equal, the limit at x = 3 does not exist.

As the condition in step 2 is not met, we do not need to proceed to step 3. Therefore, we can conclude that the function **f(x) = 5x + 2** is not continuous at x = 3.

## The Significance of Continuity

You may question why it is essential to determine if a function is continuous or not. Continuity can provide us with significant information about the behavior of a function. For instance, if a function is discontinuous at a specific point, it indicates that something significant occurred at that point.

For example, let's consider a population model with time (x) measured in years and the function given by **f(x) = 3000/x**. If we conclude that this function is not continuous at x = 0, it implies that a noteworthy event took place in the population being studied. In this scenario, it could be a sudden decline that requires further investigation.

## Types of Continuity

So far, we have only discussed continuity at a single point, but what about continuity over an interval or the entire real line? To learn more about these types of continuity, take a look at "Continuity over an Interval" and "Theorems of Continuity."

## Key Takeaways

- A function is continuous if the limit of the function at a given point is the same as the function value at that point.
- To determine continuity at a point, we need to check that the function is defined at the point, the limit from both sides is equal, and the function value aligns with the limit value.
- A function that is discontinuous at a point is considered to be discontinuous.
- Continuity is crucial in comprehending the behavior of a function and can provide insight into significant events.

## In Conclusion

To summarize, continuity is a fundamental concept in calculus that can offer valuable information about a function's behavior. By following a simple three-step process, we can determine if a function is continuous at a given point. It is essential to have a strong grasp on continuity before moving on to more complex mathematical concepts.