How to Find Discontinuity of a Function – A Step-by-Step Guide

To find the discontinuity of a function, I first examine points where the function is not defined, such as values that result in a division by zero.

Understanding discontinuity is essential because it reveals where a function breaks, which is crucial for an accurate analysis of its behavior.

For instance, with a rational function, like $\frac{x+3}{x-2}$, I look for values of ( x ) that cause the denominator to be zero, as these are the points of discontinuity.

A graph with a function line that abruptly changes direction, indicating a point of discontinuity

Continuity and discontinuity are foundational concepts in calculus that describe the behavior of functions on their domains.

A function is known to be a continuous function when, for every point ( c ) within its domain, the limit as ( x ) approaches ( c ) is equal to the function’s value at ( c ). Consequently, a discontinuous point is where this condition fails—either due to a jump, an infinite behavior, or a missing point in the function.

To effectively analyze a function for discontinuity, I also use limits to check if a function approaches different values from the left and right as ( x ) approaches a particular point.

I always keep my analysis precise and logical, and I find joy in uncovering the intricate ways functions behave. It’s like detective work where each calculation reveals more about the function’s story.

Ready to play detective with me? Let’s unravel the mysteries of discontinuity together!

Algebraic Methods for Finding Discontinuities


When examining functions algebraically to detect discontinuities, I look for points where the function is not continuous.

A function is said to be continuous on its domain if there are no breaks, holes, or jumps when graphed. However, algebraically, these interruptions in continuity can often be found through several methods.

One common type of discontinuity is the removable discontinuity, typically occurring when a certain value in the denominator matches a factor in the numerator, thus making the function value undefined for that specific input.

Such discontinuities can sometimes be “removed” if the common factor is canceled out. For instance, the function $ f(x) = \frac{x^2-4}{x-2} $ has a removable discontinuity at $ x=2 $ because $ x^2-4 $ can be factored to $ (x-2)(x+2) $, eliminating the common term.

TermFactored FormCancelationDiscontinuity Point
$ x^2-4 $$ (x-2)(x+2) $$ (x+2) $$ x=2 $

A jump discontinuity occurs when the limit of the function as the variable approaches the point from either side are not equal. This results in a function suddenly “jumping” from one value to another.

For infinite discontinuities or vertical asymptotes, occur when the function approaches infinity as the variable approaches a certain value.

For example, $ f(x) = \frac{1}{x} $ has an infinite discontinuity at $ x=0 $. The vertical line $ x=0 $ is a vertical asymptote because as $ x $ approaches zero, the function’s value grows without bounds.

Lastly, if I’m dealing with a polynomial, I know they are continuous over all real numbers, which means I won’t find any discontinuities unless they are piecewise-defined functions with different polynomial expressions over different intervals.

Graphical Analysis of Discontinuity


When I examine the graph of a function to identify discontinuities, I look for specific types of irregularities that indicate that the function is not continuous at those points. Three main types of discontinuities can be visually detected: holes, jumps, and asymptotes.

I look for holes in a graph, which are points where a function is not defined. Mathematically, a hole occurs at a point ( x = a ) if the limit of the function exists as ( x ) approaches ( a ), but the function does not have a value at ( a ).

They typically appear as small circles or dots where the function does not touch. Jump discontinuities occur when there is a sudden change in the value of the function.

This manifests on a graph as two sections that do not connect, often because the function jumps from one value to another as it crosses a certain point along the ( x )-axis. Imagine a step on a staircase where the function abruptly changes from one value to another, making a vertical leap in the process.

Lastly, I inspect for asymptotes, which are lines that a graph approaches but never touches. Vertical and horizontal asymptotes are common and indicate where a function grows without bounds or where the limit of the function approaches a particular value.

An example of a vertical asymptote can be seen in the graph of $ \frac{1}{x}$, where the function shoots off to infinity as ( x ) approaches zero.

In the table below, I’ve summarized the visual cues for each type of discontinuity:

Discontinuity TypeGraphical Feature
HoleA point missing from the curve; often marked with a dot
JumpA sudden vertical leap in the graph
AsymptoteA line the graph approaches but never touches

To discern these features more clearly, I may need to zoom in on the graph or look at its behavior from different angles. Recognizing these discontinuities by analyzing the graph can give me a deeper understanding of the function’s behavior.

Practical Examples and Solutions

When I encounter a function in calculus, I always start by checking its continuity. Let’s say that I have a piecewise function, and I suspect it might not be continuous at some point.

My first step is usually to graph the function if I can. I look for breaks in the graph, but when a graph isn’t available or isn’t clear, I move on to algebra.

Here is an example. Consider the function defined by:

$$ f(x) = \begin{cases} x^2 & \text{if } x < 1 \ 2x – 1 & \text{if } x \geq 1 \end{cases} $$

I check for discontinuity at ( x = 1 ) because that’s where the definition of the function changes. The left-hand limit as ( x ) approaches 1 is ( \lim_{{x \to 1^-}} x^2 = 1 ). The right-hand limit is ( \lim_{{x \to 1^+}} (2x – 1) = 1 ). Both limits are equal and the function value is ( f(1) = 1 ). So, the function is continuous at ( x = 1 ).

If the limits didn’t match, or if ( f(1) ) had a different value (or didn’t exist), we’d have a discontinuity.

For rational functions, like

$$ g(x) = \frac{2x}{x-3}, $$

I look for discontinuities at places where the denominator equals zero, here at ( x = 3 ). Since $\lim_{{x \to 3}} g(x) $ is undefined, there’s a discontinuity at ( x = 3 ).

Here’s a step-by-step process for checking discontinuities:

  1. Identify where the function changes form or the denominator equals zero.
  2. Calculate the left-hand and right-hand limits at those points.
  3. Compare these limits to the actual value of the function (if it exists).

For instant feedback, I sometimes use a calculator with graphing capabilities to trace the function’s behavior. This helps me visualize and verify conditions for continuity or identify types of discontinuities, such as jump or infinite discontinuities.


In assessing the continuity of a function, I’ve explored several types of discontinuities.

To recall, a point of discontinuity is present when the limits from the right and left do not match, that is, if $\lim_{x \to a^+}f(x) \neq \lim_{x \to a^-}f(x)$.

Infinite discontinuities occur when the function’s value tends towards infinity, as in the case of $\tan(x)$ at $x = \pm\frac{\pi}{2}, \pm\frac{3\pi}{2},…$. We also have removable discontinuities, which is when a function is not defined at a point but could be made continuous by defining or redefining it at that point.

Finding discontinuities is crucial for understanding the behavior of a function and for the accurate interpretation of graphs and practical data.  By applying the concepts I’ve outlined, identifying where a function is not continuous becomes a structured process.

Remember, exploring these points can lend insights into the nature of the function and potentially reveal areas where further analysis or a revised approach is warranted.

As a final note, always verify the function’s domain first, as it sets the stage for where I need to inspect for discontinuities.

Recognizing the types of discontinuities and understanding their characteristics has been my focus, and I trust these insights will aid in your continuous exploration of mathematical functions.