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  • Basics of Discontinuity

  • Types of Discontinuity

  • What is Removable Discontinuity?

  • Identifying Removable Discontinuity

  • How to "Remove" a Discontinuity

  • The Importance of Removable Discontinuity in Calculus

  • Practice Problems

  • Conclusion

Home > Resources > Removable Discontinuity: In-Depth Guides with Examples

Removable Discontinuity: In-Depth Guides with Examples

Mathematics is a universe of numbers, shapes, and patterns, but it's also a realm of abstract concepts and their intriguing properties. Among these are the ideas of continuity and discontinuity, which play crucial roles, especially in calculus.

Discontinuity, in particular, can often seem daunting to students due to its abstract nature. However, with a focused exploration, it becomes not just understandable but also fascinating.

This article zeroes in on a specific type of discontinuity that can be "fixed" or "removed" - aptly named the removable discontinuity. Our journey will decode its mysteries, making it accessible and manageable for learners at all levels.

Basics of Discontinuity

To understand discontinuity, we first need to grasp what it means for a function to be continuous. Imagine drawing a curve on a piece of paper without lifting your pen; if you can do this for the entire curve, the function represented by the curve is continuous.

In more formal terms, a function \(f(x)\) is continuous at a point \(x = a\) if the following three conditions are met:

1. The function is defined at \(x = a\); that is, \(f(a)\) exists.

2. The limit of \(f(x)\) as \(x\) approaches \(a\) exists.

3. The limit of \(f(x)\) as \(x\) approaches \(a\) is equal to \(f(a)\).

Mathematically, this can be stated as \(\lim_{x \to a} f(x) = f(a)\).

A discontinuity occurs when any of these conditions are not met. It means there's a "break" in our curve, which could manifest as a gap, a jump, or even an infinite leap.

Types of Discontinuity

Discontinuities come in various types, each with its unique characteristics. They are generally classified into three main categories:

1. Removable Discontinuity - This occurs when a function is not defined at a point, but its limit exists. The "gap" can be "filled," making the function continuous.

2. Jump Discontinuity - At a point of jump discontinuity, a function has a sudden leap or jump. The limits from the left and the right do not match, indicating a distinct separation in the function's path.

3. Infinite (or Essential) Discontinuity - This type involves a function going towards infinity at a certain point. The limits do not exist, showcasing a vertical asymptote or a drastic, unbounded separation.

Our focus, removable discontinuity, highlights an intriguing aspect of mathematical functions - some discontinuities can be "corrected," enhancing our understanding and application of these functions.

What is Removable Discontinuity?

A removable discontinuity occurs at a point on a function where the function is not defined, yet the limit as we approach that point exists. Mathematically, for a function \(f(x)\) with a removable discontinuity at \(x = a\), we can say:

- \(f(a)\) is undefined or does not equal the limit as \(x\) approaches \(a\).

- However, \(\lim_{x \to a} f(x)\) exists.

A classic example of removable discontinuity can be represented by the function:

\[ f(x) = \frac{x^2 - 1}{x - 1} \]

At \(x = 1\), the function seems undefined because it results in a \(0/0\) form. Yet, if we simplify the expression to \(f(x) = x + 1\), except at \(x = 1\), we reveal that the limit as \(x\) approaches 1 does exist and is equal to 2. The discontinuity at \(x = 1\) can be "removed" by redefining the function at this point to make it continuous.

Identifying Removable Discontinuity

Identifying removable discontinuities in mathematical functions requires a keen understanding of limits and function definitions. Here's a step-by-step approach to recognizing a removable discontinuity:

1. Examine the Function Definition: Start by looking for points where the function might not be defined. These can be spots where the function’s denominator is zero or where a function piecewise changes its formula.

2. Calculate the Limit: Compute the limit of the function as \(x\) approaches the point of interest from both the left and the right. If these two limits exist and are equal, the overall limit of the function at that point exists.

3. Compare the Limit and Function Value: If the limit exists but the function is not defined at that point, or the function’s value at that point differs from the limit, there is a removable discontinuity.

For example, consider the function \( f(x) = \frac{x^2 - 4}{x - 2} \). At \( x = 2 \), the function appears to be undefined. However, if we simplify the expression, we get \( f(x) = x + 2 \), for all \(x\) except \(x = 2\).

Calculating the limit as \(x\) approaches 2 gives us 4, which suggests that if \( f(2) \) were defined as 4, the function would be continuous. This indicates a removable discontinuity at \(x = 2\).

How to "Remove" a Discontinuity

The process of removing a discontinuity involves adjusting the function so that it becomes continuous at the formerly discontinuous point. This usually means redefining the function value at the point of discontinuity to match the limit.

Following our identification steps, let's see how this is done:

1. Simplify the Function (If Needed): For rational functions, like our previous examples, simplify the function to get rid of the zero in the denominator, if possible.

2. Define the Function at the Point of Discontinuity: Redefine the function at the point of discontinuity using the limit value at that point. This step "fills the gap" in the graph.

Using the previous example \( f(x) = \frac{x^2 - 4}{x - 2} \), we first simplify the function to \(f(x) = x + 2\), which is valid for all \(x\) except \(x = 2\). To remove the discontinuity at \(x = 2\), we redefine \(f(x)\) to be:\[ f(x) = \begin{cases} x + 2 & \text{for } x \neq 2 \\ 4 & \text{for } x = 2 \end{cases} \]

This redefinition makes \(f(x)\) continuous at \(x = 2\), effectively removing the discontinuity.

By "removing" a discontinuity in this way, we ensure that the function can now be graphed without lifting the pen off the paper, making the function continuous across its domain.

The Importance of Removable Discontinuity in Calculus

Removable discontinuities hold a unique place in calculus for several reasons, underlining the importance of a thorough understanding of this concept:

1. Limits: The calculus concept of limits is foundational, and removable discontinuities offer a clear illustration of how limits can approach a value that the function itself does not take. This understanding is crucial for the study of limits and continuity.

2. Derivatives: When calculating derivatives, removable discontinuities can initially seem to pose a problem. However, by redefining functions to "remove" these discontinuities, we can find derivatives at points that might not have been possible otherwise.

3. Integral Calculus: In integral calculus, understanding the nature of discontinuities, including removable ones, is essential for correctly setting up and evaluating definite integrals, especially when considering the area under a curve.

4. Real-World Applications: Many real-world phenomena that can be modeled by functions with removable discontinuities. Understanding how to handle these discontinuities allows for more accurate modeling of natural events and processes in engineering, physics, and economics.

Practice Problems

To further ground your understanding of removable discontinuities, here are a few practice problems to work through:

1. Identify and Remove the Discontinuity:

- Given \( f(x) = \frac{x^2 - 9}{x - 3} \), identify if there's a removable discontinuity. If so, redefine the function to remove it.

2. Analysis of a Piecewise Function:

- Consider the function defined by:\[ f(x) = \begin{cases} x^2 - 4x + 4, & \text{for } x < 2 \\ ax^2 - bx + 4, & \text{for } x \geq 2 \end{cases} \]

For what values of \(a\) and \(b\) would there be a removable discontinuity at \(x = 2\)? Remove the discontinuity.

3. Exploring Limits and Continuity:

- Evaluate the limit \(\lim_{x \to 5} \frac{x^2 - 25}{x - 5}\) and discuss the presence of any removable discontinuity. How would you make the function continuous at \(x = 5\)?


1. \( f(x) = \frac{x^2 - 9}{x - 3} \) simplifies to \( f(x) = x + 3 \), except at \(x = 3\). To remove the discontinuity at \(x = 3\), redefine \(f(3) = 6\).

2. When \(x < 2\), \(f(x) = (x - 2)^2\). For \(x \geq 2\), to avoid a discontinuity, the formula must match the value of the function just before \(x = 2\), which means \(a = 1\) and \(b = 4\) to create a continuous function across \(x = 2\).

3. The limit \(\lim_{x \to 5} \frac{x^2 - 25}{x - 5}\) simplifies to \(\lim_{x \to 5} (x + 5) = 10\), indicating a removable discontinuity at \(x = 5\). The function can be made continuous by defining it as \(f(5) = 10\).


Removable discontinuities serve as a fascinating intersection between theoretical mathematics and practical application.

Through the exploration of limits, the process of identifying and "removing" discontinuities, and understanding their significance in calculus, we gain deeper insights into the continuous nature of the world around us, modeled through mathematics.

Whether it's in the realm of academic exploration or solving real-world problems, the knowledge of how to handle these discontinuities enriches our mathematical toolkit, allowing for greater precision and understanding.

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