17calculus
Limits Derivatives Integrals Infinite Series Parametrics Polar Coordinates Conics
Limits
Epsilon-Delta Definition
Finite Limits
One-Sided Limits
Infinite Limits
Trig Limits
Pinching Theorem
Indeterminate Forms
L'Hopitals Rule
Limits That Do Not Exist
Continuity & Discontinuities
Intermediate Value Theorem
Derivatives
Power Rule
Product Rule
Quotient Rule
Chain Rule
Trig and Inverse Trig
Implicit Differentiation
Exponentials & Logarithms
Logarithmic Differentiation
Hyperbolic Functions
Higher Order Derivatives
Differentials
Slope, Tangent, Normal...
Linear Motion
Mean Value Theorem
Graphing
1st Deriv, Critical Points
2nd Deriv, Inflection Points
Related Rates Basics
Related Rates Areas
Related Rates Distances
Related Rates Volumes
Optimization
Integrals
Definite Integrals
Integration by Substitution
Integration By Parts
Partial Fractions
Improper Integrals
Basic Trig Integration
Sine/Cosine Integration
Secant/Tangent Integration
Trig Integration Practice
Trig Substitution
Linear Motion
Area Under/Between Curves
Volume of Revolution
Arc Length
Surface Area
Work
Moments, Center of Mass
Exponential Growth/Decay
Laplace Transforms
Describing Plane Regions
Infinite Series
Divergence (nth-Term) Test
p-Series
Geometric Series
Alternating Series
Telescoping Series
Ratio Test
Limit Comparison Test
Direct Comparison Test
Integral Test
Root Test
Absolute Convergence
Conditional Convergence
Power Series
Taylor/Maclaurin Series
Radius of Convergence
Interval of Convergence
Remainder & Error Bounds
Fourier Series
Study Techniques
Choosing A Test
Sequences
Infinite Series Table
Practice Problems
Exam Preparation
Exam List
Parametrics
Parametric Curves
Parametric Surfaces
Slope & Tangent Lines
Area
Arc Length
Surface Area
Volume
Polar Coordinates
Converting
Slope & Tangent Lines
Area
Arc Length
Surface Area
Conics
Parabolas
Ellipses
Hyperbolas
Conics in Polar Form
Vectors Vector Functions Partial Derivatives/Integrals Vector Fields Laplace Transforms Tools
Vectors
Unit Vectors
Dot Product
Cross Product
Lines In 3-Space
Planes In 3-Space
Lines & Planes Applications
Angle Between Vectors
Direction Cosines/Angles
Vector Projections
Work
Triple Scalar Product
Triple Vector Product
Vector Functions
Projectile Motion
Unit Tangent Vector
Principal Unit Normal Vector
Acceleration Vector
Arc Length
Arc Length Parameter
Curvature
Vector Functions Equations
MVC Practice Exam A1
Partial Derivatives
Gradients
Directional Derivatives
Lagrange Multipliers
Tangent Plane
MVC Practice Exam A2
Partial Integrals
Describing Plane Regions
Double Integrals-Rectangular
Double Integrals-Applications
Double Integrals-Polar
Triple Integrals-Rectangular
Triple Integrals-Cylindrical
Triple Integrals-Spherical
MVC Practice Exam A3
Vector Fields
Curl
Divergence
Conservative Vector Fields
Potential Functions
Parametric Curves
Line Integrals
Green's Theorem
Parametric Surfaces
Surface Integrals
Stokes' Theorem
Divergence Theorem
MVC Practice Exam A4
Laplace Transforms
Unit Step Function
Unit Impulse Function
Square Wave
Shifting Theorems
Solve Initial Value Problems
Prepare For Calculus 1
Ready For Calculus 2?
Trig Formulas
Describing Plane Regions
Parametric Curves
Linear Algebra Review
Word Problems
Mathematical Logic
Calculus Notation
Simplifying
Practice Exams
17calculus on YouTube
More Math Help
Tutoring
Tools and Resources
Academic Integrity
Learning/Study Techniques
Math/Science Learning
Memorize To Learn
Music and Learning
Note-Taking
Motivation
Instructor or Coach?
Books
Math Books
How To Read Math Books

You CAN Ace Calculus

17calculus > limits

Limits

on this page: ► limit notation     ► basic idea of limits     ► limit key     ► limit laws     ► difference between a limit going to ±∞ and a limit that doesn't exist

Limits form the basis of all of calculus. So it is important to understand and be able to use limits. This topic is going to stretch your mind a bit but if you stick with it, you will get it.

Finite Limits, Infinite Limits, Limits At Infinity . . . Terminology Explained

The use of the terms finite limits, infinite limits and limits at infinity are used differently in various books and your instructor may have their own idea of what they mean. In this panel, we will try to break down the cases and explain the various ways these terms can be used as well as how we use them here at 17calculus.

When we talk about limits, we are looking at the \(\displaystyle{ \lim_{x \to c}{f(x)} = L }\). The various terms apply to the description of \(c\) and \(L\) and are shown in the table below. The confusion lies with the terms finite limits and infinite limits. They can mean two different things.

\(\displaystyle{ \lim_{x \to c}{f(x)} = L }\)

when

term(s) used

\(c\) is finite

limits approaching a finite value or finite limits

\(c\) is infinite \(\pm \infty\)

limits at infinity or infinite limits

\(L\) is finite

finite limits

\(L\) is infinite \(\pm \infty\)

infinite limits

You can see where the confusion lies. The terms finite limits and infinite limits are used to mean two different things, referring to either \(c\) or \(L\). It is possible to have \(c = \infty\) and \(L\) be finite. So is this an infinite limit or a finite limit? It depends if you are talking about \(c\) or \(L\).

How 17calculus Uses These Terms
The pages on this site are constructed based on what \(c\) is, i.e. we use the terms finite limits and infinite limits based on the value of \(c\) only ( using the first two rows of the table above and ignoring the last two ). This seems to be the best way since, when we are given a problem, we can't tell what \(L\) is until we finish the problem, and therefore we are unable to determine what type of problem we have and know what techniques to use until we are done with the problem.

Important: Make sure and check with your instructor to see how they use these terms.

Limit Notation

First, let's talk a bit about limit notation. To understand why we need to discuss notation, read this next panel on why notation is important in calculus.

Why Notation is Important in Calculus

Using correct notation is extremely important in calculus. If you truly understand calculus, you will use correct notation. Take a few extra minutes to notice and understand notation whenever you run across a new concept. Start using correct notation from the very first.

You may not think this is important. However, if your current (or previous) teacher doesn't require correct notation, learn it on your own. You may (and probably will) get a teacher in the future that WILL require correct notation and this will cause you problems if you don't learn it now. It is much easier to learn it correctly the first time than to have to correct your notation later, after you have been doing it incorrectly for a while.

Not only is it important in class to use correct notation, when you use math ( or any other subject that uses special symbols ) in your career, you will need to be able to communicate what you mean. Without correct notation, your ideas could be misunderstood. It's a lot like speaking English ( or whatever language you use regularly ) or speaking a variant that has meaning only to you. You will be misunderstood and it may even affect your ability to keep a job.

So, just decide to start using correct notation now. It's not that hard and it will pay off in the long run.

When writing a limit, we use the notation \(\displaystyle{ \lim_{x \rightarrow c}{~f(x)} }\). There are three important parts to this notation that must all exist for this notation to have meaning.
1. The three letter abbreviation 'lim'. This tells you that you have a limit.

2. The notation \( x \rightarrow c \). This is important because it tells you two things; the variable that the limit applies to, 'x', and the value it is approaching, 'c'. Leaving this off when using limit notation leaves the reader guessing the variable and the value.

3. The function itself, 'f(x)'. Without this you don't know what function the limit is being applied to.

It is important that you have all three parts at all times when you use this notation. A good calculus teacher will encourage this by taking off points if you leave off any part.

Note: In type-written documents, including your textbook, you may see the limit written as \( \lim_{x \rightarrow c}{~f(x)} \). It is written this way to save space. However, it is not okay to write it this by hand. You need to write it as \(\displaystyle{ \lim_{x \rightarrow c}{~f(x)} }\) with the \(x \to c\) directly underneath lim.

Basic Idea of Limits

Now that you understand the notation related to limits, let's watch a few videos explaining the basic idea of limits and how to work with them. It is important to watch the first two videos to get a full understanding.

This first video is a great introduction video explaining the basic idea of limits and how to get started.

PatrickJMT: What is a Limit? Basic Idea of Limits

This next video clip has a great explanation of limits using some examples.

Krista King Math - Limits and Continuity

The rest of this page contains a few topics related to limits in general. To study specific topics in depth, you can find links in the menu above. These individual pages contain discussion, videos and practice problems. However, before you go there, the next few sections contain important background information you need to understand the other topics. So it will help you to go through these sections.

Limit Key

One key that you need to remember about limits is when you use the limit notation \[ \lim_{x \rightarrow c}{ ~f(x) } \] this means that x APPROACHES c but is never equal to c. This means x can get as close as it wants to but it will never actually equal c. That seems simple enough but it is extremely important to remember. There are many times when you can determine the limit by substituting x for c to calculate f(c). However, those are special cases that require special conditions and is not true in every case. There is probably a theorem in your textbook that tells the special conditions that must exist for you to be able to apply this.

Here is an explanation of how this concept is written mathematically. Look more carefully at the definition of the limit at the top of the page. Notice that it requires \( \delta \gt 0 \). This means that \( |x-c| > 0 \) and, therefore, x can never equal c.

I know this seems like a minor point, but it isn't. If you remember this, you will have a good start on your way to understanding limits.

Limit Laws

In general, limits follow the algebra rules as you would expect. However, as with all of higher math, we need to explicitly write out the rules, so that we know what we can do and what we can't do. So, here are some basic limit laws.
Note: In all cases below, when we state that a variable is a constant, that means it is a real number and not \(\infty\) or \(-\infty\). However, these rules also apply when \( x \to \infty \) or \( x \to -\infty \).
In these equations, we assume that
1. \(b\), \(c\) and \(k\) are constants
2. \(\displaystyle{ \lim_{x\to c}{~f(x)} = L }\) and \(\displaystyle{ \lim_{x\to c}{~g(x)} = M }\)
3. \(n\) is a positive integer

Constant Rule

\(\displaystyle{ \lim_{x\to c}{ ~b } = b }\)

Identity Rule

\(\displaystyle{ \lim_{x\to c}{~x} = c }\)

Operational Identities

1. Constant Multiple Rule

\(\displaystyle{ \lim_{x \to c}{[k\cdot f(x)]} = }\) \(\displaystyle{ k \cdot \lim_{x \to c}{f(x)} = kL }\)

2. Sum/Difference Rule

\(\displaystyle{ \lim_{x\to c}{[f(x) \pm g(x)]} = }\) \(\displaystyle{ \lim_{x\to c}{~f(x)} \pm \lim_{x\to c}{~g(x)} = }\) \(\displaystyle{ L \pm M }\)

3. Multiplication Rule

\(\displaystyle{ \lim_{x\to c}{[f(x) \cdot g(x)]} = }\) \(\displaystyle{ \lim_{x\to c}{~f(x)} \cdot \lim_{x\to c}{~g(x)} = }\) \(\displaystyle{ L \cdot M }\)

4. Division Rule

\(\displaystyle{ \lim_{x\to c}{[f(x)/g(x)]} = }\) \(\displaystyle{ \frac{\lim_{x\to c}{~f(x)}}{\lim_{x\to c}{~g(x)}} = }\) \(\displaystyle{ \frac{L}{M} ~~~ M \neq 0 }\)

Power Rule

\(\displaystyle{ \lim_{x\to c}{[f(x)]^n} = }\) \(\displaystyle{ \left[ \lim_{x\to c}{~f(x)} \right]^n }\)

Difference Between A Limit Going To ±∞ and A Limit That Doesn't Exist

Many people get confused between the case when a limit goes to infinity (or negative infinity) and when a limit does not exist. And there is a good reason for the confusion. Many discussions I've read do not separate the two cases. But they are different.

when a limit DOES exist
When a limit goes to positive or negative infinity, the limit DOES exist. The limit is exactly that, positive or negative infinity.

when a limit DOES NOT exist
There is only one case when a limit doesn't exist: when the limit is different from the left than it is from the right. This concept requires understanding one-sided limits, which you can find on this page. There are also videos on that page showing examples of when the limit doesn't exist.

For more detail including graphs, see the substitution section on the finite limits page. And, as usual, check with your instructor to see how they define limits that do not exist.

Okay, now you are ready to go to the next topic: the epsilon-delta definition of the limit.

next: \(\epsilon\)-\(\delta\) limit definition →

faq: What does 'indeterminate' mean?

What does 'indeterminate' mean?

The word 'indeterminate' usually shows up when discussing limits and it means 'cannot be determined'. For example, when you take a limit and get the result \( 0/0 \), this is indeterminate, meaning the limit could be anything and cannot be determined with the given information.

Many times, you can determine the limit but in order to do so, you need to alter the function using algebra, trig or L'Hôpital's Rule to put it in a form so that is no longer indeterminate. You can find plenty of examples (practice problems) on the finite limits page, infinite limits page and L'Hôpital's Rule page.

You can find more information on 17Calculus: Indeterminate Forms (including a table listing most indeterminate forms you will see in calculus).

like? 2

Search 17Calculus

Real Time Web Analytics
menu top search
36
17
menu top search 17