Basics of Limit Calculus: Definition, Rules, Methods, and Calculations

In the fascinating world of mathematics, understanding limits is a fundamental concept. A limit represents the value a function approaches as its input variable gets closer and closer to a particular point. The limit helps us examine the behavior of functions at critical points and aids in making predictions about their overall characteristics. 

Limit is a key concept in calculus; it is used in almost all major and important concepts, such as differentiation and integrals. A limit is a point or stage beyond which something cannot proceed. Something that confines, limits, or binds is a limit.

Limits provide us with insights into various aspects of functions and their graphs. In this article, we will elaborate on the concept of limits. We will discuss fundamental rules that are useful for the computation of limits of different functions. We will also discuss some limits evaluating methods as well as a few examples. 

What are Limits?

Formally, the limit of a function ‘f(x)’ as ‘x’ approaches ‘a’ is defined as follows:

Lim f(x) = L as x approaches a.

This implies that for any given positive number ‘ε’ (epsilon), there exists a corresponding positive number ‘δ’ (delta) such that:

|f(x) – L| < ε whenever 0 < |x – a| < δ.

In simpler terms, as ‘x’ gets arbitrarily close to ‘a,’ the function ‘f(x)’ gets arbitrarily close to ‘L.’

Limit Notation and Terminology:

In mathematical notation, the limit symbol is represented by “lim.” For example, “limx🡪2 f(x)” denotes the limit of the function “f(x)” as “x” approaches the value “2.”

Discontinuity and Asymptotes:

A function is discontinuous at a point if the limit does not exist at that point. Asymptotes are lines that a graph approaches but never touches.

Basic Limit Rules

Understanding the rules governing limits is essential for solving complex mathematical problems involving various functions. Here are some fundamental limit rules:

Sum ruleLimx🡪c (f(x) + g(x)) = Limx🡪c f(x) + Limx🡪c g(x)L + M 
Difference rule Limx🡪c (f(x) – g(x)) = Limx🡪c f(x) – Limx🡪c g(x)L – M 
Constant multiple rule Limx🡪c a*f(x) = a* Limx🡪c (f(x)a L
Product ruleLimx🡪c (f(x) * g(x)) = Limx🡪c f(x) * Limx🡪c g(x)L.M
Quotient rule Limx🡪c (f(x) / g(x)) = Limx🡪c f(x) / Limx🡪c g(x)L / M for M ≠ 0
Constant ruleLimx🡪c a = a

Method of Evaluating Limits:

Below are the methods for evaluating limits

  1. Direct Substitution Method:

The direct substitution method involves plugging the value of the point “c” directly into the function and evaluating it. This method works for most simple cases.

  1. Factoring and Cancelling Method:

When faced with indeterminate forms (0/0 or ∞/∞), factoring and canceling common factors can help simplify the function and make it easier to evaluate the limit.

  1. Rationalizing Method:

The rationalizing method is useful when dealing with limits involving square roots or cube roots. It involves multiplying the function by its conjugate to eliminate square roots from the denominator.

Types of Limit Calculus

  1. One-Sided Limits:

In certain situations, we may only be concerned with the behavior of a function from one direction (left or right) as it approaches a point. These are known as one-sided limits.

  1. Limits at Infinity:

In some cases, a function may approach infinity or negative infinity as it approaches a particular point. These are known as infinite limits. 

When a function approaches infinity or negative infinity as the input grows without bound, we refer to it as a limit at infinity. Limits help us understand the behavior of functions as they approach infinity or negative infinity, providing insights into asymptotic behaviors.

Examples of Limits:

Let’s explore some examples to solidify our understanding of limits:

Example 1:

Find the limit of the function f(x) = 2x2 – 3x + 1 as x approaches 4 applying suitable limit rules.


Step 1: Given data

Function = f(x) = 2x2 – 3x + 1 as x approaches 4.

Step 2: Place the values

limx🡪4 f(x) = limx🡪4 2x2 – limx🡪4 3x + limx🡪4 1 (sum & difference rule)

limx🡪4 f(x) = 2 limx🡪4 x2 – 3 limx🡪4 x + limx🡪4 1 (constant multiple rule)

limx🡪4 f(x) = 2 * (4)2 – 3 * 4 + 1 (constant rule)

limx🡪4 f(x) = 2 * 16 – 12 + 1  

limx🡪4 f(x) = 32 – 12 + 1

limx🡪4 f(x) = 21

A limit calculator with steps can be used to evaluate the limit problems in a step-by-step way to avoid manual evaluations.

Example 2:

Compute the limit of the function f(x) = (x2 – 9) / (x – 3) as x approaches 3 applying suitable limit rules.


Step 1: Given data

Function = f(x) = [(x2 – 9) / (x – 3)] as x approaches 3.

Step 2: Simplify, applying the limit value.

limx🡪3 f(x) = limx🡪3 [(x2 – 9) / (x – 3)]

limx🡪3 f(x) = limx🡪3 (x2 – 9) / limx🡪3 (x – 3)     (Quotient rule)

limx🡪3 f(x) = [(3)^2 – 9) / (3 – 3)] 

limx🡪3 f(x) = (9 – 9) / (3 – 3)

limx🡪3 f(x) = 0 / 0

As we have encountered that this function answers an indeterminate 0/0 form. So, we should have to simplify it first. 

Step 3: Simplification

limx🡪3 f(x) = limx🡪3 [(x2 – 9) / (x – 3)]

limx🡪3 f(x) = limx🡪3 [(x + 3) * (x – 3) / (x – 3)]

limx🡪3 f(x) = limx🡪3 (x + 3)

Step 4: Place the values

limx🡪3 f(x) = limx🡪3 x + limx🡪3 3   (sum rule)

limx🡪3 f(x) = 3 + 3

limx🡪3 f(x) = 6 


In conclusion, limits are a fundamental concept in mathematics, providing valuable insights into the behavior of functions as they approach specific points. In this article, we have gone through the core concept of limits, significant rules, important evaluating techniques, and some examples. 

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