Factorising special double brackets (perfect squares, difference between squares)

Recognise and factorise perfect-square trinomials and differences of two squares into double brackets.

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Learning objective overview

Master Teaching Guide coverage for this objective.

Current NZC (2007)
  • NA6-6
New NZC (2026)
  • NZC26-P4-ALG-ER-K-Y10-06

Resources

  • CorbettMaths on factorising difference between squaresQuestions PDF · Answers
  • Beta: Single brackets: Ex 9.04 to Ex 9.07, pgs 171 to 174

Terminology

  • difference between two squares
  • perfect square
  • factorise
  • highest common factor (hcf)
  • quadratic
  • difference of two squares
  • coefficient
  • constant term

Task goals

  • Factorise a perfect-square trinomial with a leading coefficient of 1, such as $x^2+6x+9$, into $(x+a)^2$ form.
  • Factorise a difference of two squares with a leading coefficient of 1, such as $x^2-16$, into $(x-a)(x+a)$ form.
  • Fill in a missing number in a partially-given perfect-square or difference-of-squares factorisation, such as $x^2+12x+36=(x+\square)^2$ or $p^2-64=(p-\square)(p+\square)$.
  • Factorise a perfect-square trinomial or difference of two squares where the leading coefficient is greater than 1, such as $4y^2+12y+9$ or $25p^2-1$.
  • Decide whether a given factorisation is correct, or identify which of four expressions does not belong with the others.
  • Factorise fully an expression requiring two applications of difference of squares, such as $x^4-81$.
  • Explain how to tell whether a quadratic is a perfect-square trinomial or a difference of two squares.
  • Given the area of a square as a quadratic expression, find an expression for its side length.

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Factorising special double brackets (perfect squares, difference between squares)

Factorising special double brackets (perfect squares, difference between squares)

Know

There are specific factorising relationships that are useful to recognise: x(x + a) = x^2 + ax; difference of two squares: (x + a)(x − a) = x^2 − a^2; square of a sum: (x + a)^2 = x^2 + 2ax + a^2; square of a difference: (x − a)^2 = x^2 − 2ax + a^2.

Statement▸
Year 10 · Algebra · Equations and relationships
NZC26-P4-ALG-ER-K-Y10-06

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