Factorising double brackets (with a leading coefficient of 1)

Factorise a quadratic expression of the form x squared + bx + c (with a leading coefficient of 1) into two brackets by finding two numbers that multiply to give c and add to give b.

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Te reo Māori terms

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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-P-Y10-01

Resources

  • Dr Austin Maths - Factorising Revision Practice GridQuestions PDF · Answers
  • CorbettMaths on factorising double brackets (when the leading coefficient is 1)Questions PDF · Answers
  • Beta: Single brackets: Ex 9.04 to Ex 9.07, pgs 171 to 174

Terminology

  • factorise
  • double brackets
  • constant
  • adds to the middle, multiplies to the constant
  • highest common factor (hcf)
  • quadratic
  • difference of two squares
  • perfect square
  • coefficient
  • constant term

Task goals

  • Factorise a quadratic $x^2+bx+c$ into two brackets when both numbers found are positive.
  • Factorise a quadratic $x^2-bx+c$ into two brackets when both numbers found are negative.
  • Fill in one or both missing numbers in a partially-given factorisation, such as $x^2+8x+15=(x+\square)(x+\square)$.
  • Factorise a quadratic where the constant term is negative, so the two brackets have one positive and one negative number, such as $x^2+4x-12$ or $x^2-3x-10$.
  • Decide whether a given factorisation is correct, or identify which of four expressions does not belong with the others.
  • Explain why the two numbers used in the brackets must add to $b$ and multiply to $c$ in $x^2+bx+c$.
  • Given the area of a rectangle as a quadratic expression and one side as a binomial factor, find the expression for the other side.

Where this fits

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Factorising double brackets (with a leading coefficient of 1)

Factorising double brackets (with a leading coefficient of 1)

Do

Simplifying and manipulating algebraic expressions involving sums, products, differences, and positive integer powers, by: collecting like terms; factorising using common factors; factorising quadratic expressions with a leading coefficient of 1; expanding products, including multiplying a single term by a bracketed term, and multiplying two expressions each of the form ax + b, where a and b are integers; factorising by grouping (i.e. using the distributive law) (e.g. x^2 + 2x − 8 = x^2 + 4x − 2x − 8 = x(x + 4) − 2(x + 4) = (x − 2)(x + 4))

Statement▸
Year 10 · Algebra · Equations and relationships
NZC26-P4-ALG-ER-P-Y10-01

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