Algebraic Expressions

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This Foundation GCSE scheme of work unit covers algebraic expressions in Year 9. It is the written language of algebra. Students collect like terms, simplify products, expand and factorise linear expressions, substitute, then expand and factorise quadratics, with two practice lessons on writing expressions and substitution.

Students have to see a letter as an unknown number that still obeys the rules of arithmetic. Secure notation here is what later equations, formulae, quadratics and algebraic fractions all depend on.

What Success Looks Like

A student who has secured this unit:

  • Collects like terms and leaves unlike terms uncombined.
  • Expands a bracket, including a negative multiplier, without dropping the second term.
  • Factorises an expression to the highest common factor, including a power.
  • Expands two binomials and collects the linear terms correctly.

Prerequisite Knowledge

Students should be secure with the following before beginning this unit.

  • Substitute a positive integer into a one-step formula.
  • Collect like terms in an expression such as 3a + 2a.
  • Write a simple missing-number problem using a letter.
  • Find a pair of integers that satisfy an equation in two unknowns.
  • Use the order of operations when a calculation includes a power.

Key Mathematical Ideas

Notation

The multiplication sign is dropped, so ab means a × b. Division is written as a fraction. A coefficient of 1 is not written.

Like terms

Linear, quadratic and cubic terms cannot be collected together. 3x and 3x² are not like terms.

Expression, equation, formula

An expression has no equals sign. An equation is true for particular values. A formula shows a relationship that still holds when the letters change.

Expanding brackets

Every term inside the bracket is multiplied. 2(x + 5) is 2x + 10 and −2(x + 5) is −2x − 10.

Highest common factor

Factorising is not finished until the highest common factor has been taken out. 18x + 24y is 6(3x + 4y), not 2(9x + 12y).

Working Mathematically

Fluency

  • Simplify 4a + 3b − a + 5b.
  • Expand 3(2x − 5) and factorise 12x + 18.
  • Expand (x + 4)(x − 3) and check by substituting x = 2.

Reasoning

  • Explain why 2x and 2x² cannot be collected.
  • Show that 18x + 24y is not fully factorised if the common factor is taken to be 2.
  • Distinguish an expression from an equation using 3x + 2 and 3x + 2 = 11.

Common Misconceptions with Algebraic Expressions

MisconceptionTeaching focus
Treating ab and ba as unlike terms, or writing a + b as ab.Substitute a = 3 and b = 4 into both forms so students can see they are equal or not.
Multiplying only the first term in a bracket, especially when the multiplier is negative.Draw two arrows from the −2 in −2(x + 5) onto x and onto 5.
Stopping after a partial factorisation, for example writing 18x + 24y as 2(9x + 12y).Ask ‘can the bracket still be factorised?’ after every first attempt.
Collecting the linear terms incorrectly when two brackets have been expanded.Write the four products on separate lines before any collecting happens.
Substituting into 2x² as (2x)².Evaluate 2 × 3² and (2 × 3)² on the same board and keep both answers visible.

Differentiation

Additional support

  • Write ab, ba and a × b in a single box so commutativity is visible while collecting terms.
  • Use an area grid for the first two-bracket expansion.
  • Give the common factor of 18x + 24y and ask only for the contents of the bracket.

Additional challenge

  • Factorise 12x²y + 18xy² and state the highest common factor of the coefficients and the letters.
  • Expand (x + 2)(x + 5)(x − 1) by treating the first product as a quadratic.
  • Write an expression for the area of a path around a rectangle with sides x and x + 3.

Teach This Unit with Mr Mathematics

Every lesson in this unit is already built. A Mr Mathematics membership gives you the presentation, worksheet, question generator and video tutorial for all 10 lessons, alongside the full Key Stage 3, GCSE, IGCSE and A-Level libraries.

A school membership covers every teacher in your department, so the whole scheme of work is resourced from one subscription.

Algebraic Expressions Lessons

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