Formula

Binomial Squares Pattern

The Binomial Squares Pattern is a shortcut for squaring a binomial that eliminates the need to write the binomial twice and apply FOIL. When a binomial (a+b)(a + b) or (ab)(a - b) is squared, the result is always a trinomial that follows a predictable structure. If aa and bb are real numbers:

(a+b)2=a2+2ab+b2(a + b)^2 = a^2 + 2ab + b^2

(ab)2=a22ab+b2(a - b)^2 = a^2 - 2ab + b^2

The pattern can be remembered as a three-step procedure:

  1. Square the first term — the first term of the trinomial is a2a^2.
  2. Square the last term — the last term of the trinomial is b2b^2.
  3. Double their product — the middle term is 2ab2ab (positive when the binomial uses addition, negative when it uses subtraction).

This pattern emerges from the FOIL method. When squaring a binomial such as (x+9)2(x + 9)^2, the expression means (x+9)(x+9)(x + 9)(x + 9). Applying FOIL gives x2+9x+9x+81x^2 + 9x + 9x + 81, and combining like terms yields x2+18x+81x^2 + 18x + 81. The Outer and Inner products are always identical because the two binomials being multiplied are the same, so the middle term is always double the product of the binomial's two terms.

A numerical check confirms the pattern works: (10+4)2=102+2104+42=100+80+16=196(10 + 4)^2 = 10^2 + 2 \cdot 10 \cdot 4 + 4^2 = 100 + 80 + 16 = 196, which matches the result of the standard order of operations: (14)2=196(14)^2 = 196.

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Updated 2026-05-01

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