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Square of a Binomial


The square of a binomial is an essential concept in algebra, where students learn to expand and simplify algebraic expressions. This article provides a comprehensive understanding of this topic, including its definition, key concepts, and illustrative examples. Additionally, it will discuss its real-life applications and provide practice tests and frequently asked questions to help reinforce the knowledge.

Grade Appropriateness

The square of a binomial is typically introduced in middle school (usually around 7th or 8th grade) and is further explored in high school algebra classes.

Math Domain

The square of a binomial falls under the domain of Algebra, specifically focusing on polynomial expressions and their operations.

Applicable Common Core Standards

This topic aligns with the Common Core State Standards for Mathematics, particularly the standards for Expressions and Equations in Grade 8 and Algebra I.

Definition of the Topic

The square of a binomial is the result of multiplying a binomial expression by itself. A binomial expression consists of two terms, usually in the form (a + b) or (a – b). When squaring a binomial, we follow the distributive property, resulting in a trinomial expression.

Key Concepts

Binomial: A binomial has two terms connected by a plus or minus sign.

Square/Squaring: Square means the product of a number when you multiply it by itself. For example, 9 is the square of 3. Squaring means when multiplying a number by itself. For example, the square of 6 is 36. 

Perfect Square Trinomials: Perfect square trinomials are polynomials with three terms. It is the result when you square a binomial.

Sum of Squares: (a + b)2= a2 + 2ab + b2

Difference of Squares: (a – b)2 = a2 – 2ab + b2

Discussion with Illustrative Examples

The square of a binomial is a type of special product where you always end up with a perfect square trinomial as the answer.

Squaring a binomial can be done by:

1. Using the distributive property

(a+b)2 = a(a+b) + b(a+b)
(a-b)2 = a(a-b) – b(a-b)

2. Using the formulas

(a+b)2 = a2 + 2ab + b2
(a-b)2 = a2 – 2ab + b2

Example 1

Find the square of x + 3.


Since we must square the binomial x+3, we must enclose it in parentheses and use the proper exponent, raising the second power. 

Using the distributive property, we shall have this calculation:  

(x + 3)2

= (x + 3) (x + 3)

=x(x+3) + 3(x+3)

= x2 + 3x + 3x + 9

= x2 + 6x + 9

Using the formula: 

(x + 3)2



Notice that we arrive at the same answer, and using the formula is a shortcut way of calculating the square of a binomial without applying the distributive property.

Example 2

Find the square of (2y – 5).


Using the distributive property to get the product we have,

(2y – 5)2

= (2y – 5)(2y – 5)

= 2y(2y – 5) – 5(2y – 5)

= 4y2 – 10y – 10y + 25

= 4y2 – 20y + 25

Using the formula:

(2y – 5)2

=(2y)2 – 2(2y)(5) + 52

=4y2 – 20y + 25

Examples with Solution

Example 1

Find the square of the binomial 5x+y using the distributive property.


(5x+ y)2

= (5x+ y)(5x+ y)

= 5x(5x+y) – y(5x+y)

= 25x2 + 5xy + 5xy + y2

= 25x2 + 10xy + y2

Example 2

Find (3x-4y)2 using the formula.


a=3x while b=4y. Applying the formula we have,


=(3x)2 – 2(3x)(4y) + (4y)2

=9x2 – 24xy + 16y2

Example 3

Using (a+b)2, find the value of (205)2.


Since we know that (a+b)2=a2+2ab+b2, we can have a=200 and b=5.

Hence, (205)2=(200+5)2.





Real-life Application with Solution

Problem 1

A square garden has a side length of (x + 2) meters. Find the area of the garden in terms of x.


A square’s area is equal to the square of its side length.

Area = (x + 2)2

= (x + 2)(x + 2)

= x2 + 2x + 2x + 4

= x2 + 4x + 4 

Therefore, the area of the square garden with a side length of x+2 is x2+4x+4 square meters.

Problem 2

Susan is making a square frame with side lengths of 5-3x. Calculate its area.


Area = (5-3x)2

= (5-3x)(5-3x)

= 25 – 15x – 15x + 9x2

= 25 – 30x + 9x2

The area of the square frame is 9x2 – 30x + 25 square units.

Practice Test

1. Find the square of (p + 4).

2. Find the square of (3q – 7).

3. Find the square of (5 – m).

4. Find the square of (3z + 1).

5. Find the square of (t – 6).

6. Evaluate (55)2 using a square of a binomial. 

7. Find the area of a square with side lengths (4m-2n) meters.


1. p2 + 2(p)(4) + (4)2 = p2 + 8p + 16

2. (3q)2 – 2(3q)(7) + (7)2 = 9q2 – 42q + 49

3. (5)2 – 2(5)(m) + m2 = 25 – 10m + m2

4. (3z)2 + 2(3z)(1) + (1)2 = 9z2 + 6z + 1

5. t2 – 2(t)(6) + (6)2 = t2 – 12t + 36

6. (50+5)2 = (50)2 + 2(50)(5) + (5)2 = 2500 + 500 + 25 = 3025

7. (4m-2n)2 = (4m)2 – 2(4m)(2n) + (2n)2 = 16m2 – 16mn + 4n   square meters

Frequently Asked Questions (FAQs)

Why do we need to learn the square of a binomial?

Learning the square of a binomial is essential for understanding more complex algebraic concepts, such as factoring, simplifying expressions, and solving quadratic equations.

Can the square of a binomial be negative?

The square of a binomial will always be non-negative because squaring any real number results in a non-negative value.

What is the difference between squaring a binomial and squaring a monomial?

Squaring a binomial involves multiplying a binomial expression (with two terms) by itself, resulting in a trinomial expression. On the other hand, squaring a monomial (a single term) involves multiplying the monomial by itself, resulting in another monomial with an exponent that is twice the original.

Is there a shortcut to squaring a binomial without using the distributive property?

Yes, you can use the formulas (a + b)2= a2 + 2ab + b2 and (a – b)2 = a2 – 2ab + b2 as shortcuts to square binomials without applying the distributive property.

Square of a Binomial (Wonders of the World Themed) Math Worksheets
Factoring Perfect Square Trinomials (Earth Day Themed) Math Worksheets
Multiplication of Polynomials (Universe Themed) Worksheets

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