Learn on PengiAoPS: Introduction to Algebra (AMC 8 & 10)Chapter 11: Special Factorizations

Lesson 2: Difference of Squares

In this Grade 4 AMC math lesson from AoPS: Introduction to Algebra, students learn the difference of squares factorization — the identity a² − b² = (a − b)(a + b) — and practice applying it to expressions like 4t² − 121 and z⁴ − 1. The lesson extends this technique to solving Diophantine equations by factoring expressions such as (m − n)(m + n) = 105 to find all integer solution pairs. Part of Chapter 11: Special Factorizations, this lesson builds algebraic reasoning skills essential for AMC 8 and AMC 10 competition preparation.

Section 1

Difference of Squares Pattern

Property

Difference of Two Squares.

(a+b)(ab)=a2b2(a + b)(a - b) = a^2 - b^2

Section 2

Consecutive Squares and Difference Patterns

Property

The difference between consecutive squares follows the pattern:

(n+1)2n2=2n+1(n+1)^2 - n^2 = 2n + 1

This means the difference between any two consecutive perfect squares is always an odd number.

Section 3

Difference of Squares Factorization

Property

a2b2=(a+b)(ab)a^2 - b^2 = (a + b)(a - b)

Examples

Section 4

Solving Diophantine Equations Using Difference of Squares

Property

When a Diophantine equation can be written as x2y2=nx^2 - y^2 = n, factor it as (xy)(x+y)=n(x-y)(x+y) = n and find integer solutions by examining all factor pairs of nn.

Examples

Book overview

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Chapter 11: Special Factorizations

  1. Lesson 1

    Lesson 1: Squares of Binomials

  2. Lesson 2Current

    Lesson 2: Difference of Squares

  3. Lesson 3

    Lesson 3: Sum and Difference of Cubes

  4. Lesson 4

    Lesson 4: Rationalizing Denominators

  5. Lesson 5

    Lesson 5: Simon's Favorite Factoring Trick

Lesson overview

Expand to review the lesson summary and core properties.

Expand

Section 1

Difference of Squares Pattern

Property

Difference of Two Squares.

(a+b)(ab)=a2b2(a + b)(a - b) = a^2 - b^2

Section 2

Consecutive Squares and Difference Patterns

Property

The difference between consecutive squares follows the pattern:

(n+1)2n2=2n+1(n+1)^2 - n^2 = 2n + 1

This means the difference between any two consecutive perfect squares is always an odd number.

Section 3

Difference of Squares Factorization

Property

a2b2=(a+b)(ab)a^2 - b^2 = (a + b)(a - b)

Examples

Section 4

Solving Diophantine Equations Using Difference of Squares

Property

When a Diophantine equation can be written as x2y2=nx^2 - y^2 = n, factor it as (xy)(x+y)=n(x-y)(x+y) = n and find integer solutions by examining all factor pairs of nn.

Examples

Book overview

Jump across lessons in the current chapter without opening the full course modal.

Continue this chapter

Chapter 11: Special Factorizations

  1. Lesson 1

    Lesson 1: Squares of Binomials

  2. Lesson 2Current

    Lesson 2: Difference of Squares

  3. Lesson 3

    Lesson 3: Sum and Difference of Cubes

  4. Lesson 4

    Lesson 4: Rationalizing Denominators

  5. Lesson 5

    Lesson 5: Simon's Favorite Factoring Trick