Formula

Product of Conjugates Pattern

The Product of Conjugates Pattern is a shortcut for multiplying a conjugate pair — two binomials of the form (a+b)(a + b) and (ab)(a - b). If aa and bb are real numbers:

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

The pattern follows a two-step procedure:

  1. Square the first term — the first term of the result is a2a^2.
  2. Square the last term and subtract it — the result is a2b2a^2 - b^2.

The product is always a binomial, not the trinomial that FOIL typically produces. This occurs because the Outer and Inner products from FOIL are equal in magnitude but opposite in sign, so they always cancel to zero. For example, applying FOIL to (x9)(x+9)(x - 9)(x + 9) gives x2+9x9x81x^2 + 9x - 9x - 81; the middle terms +9x+9x and 9x-9x sum to zero, leaving x281x^2 - 81. Similarly, (y8)(y+8)=y264(y - 8)(y + 8) = y^2 - 64 and (2x5)(2x+5)=4x225(2x - 5)(2x + 5) = 4x^2 - 25.

The expression a2b2a^2 - b^2 is called a difference of squares because it is the difference of two squared terms. Although FOIL can always be used to multiply conjugates directly, applying this pattern makes the work faster.

Image 0

0

1

Updated 2026-04-29

Contributors are:

Who are from:

Tags

OpenStax

Elementary Algebra @ OpenStax

Ch.6 Polynomials - Elementary Algebra @ OpenStax

Algebra

Math

Ch.7 Factoring - Elementary Algebra @ OpenStax

Ch.9 Roots and Radicals - Elementary Algebra @ OpenStax

Prealgebra

Intermediate Algebra @ OpenStax

Ch.5 Polynomials and Polynomial Functions - Intermediate Algebra @ OpenStax

Related
Learn After