IGCSE Higher Algebraic Manipulation

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Algebraic Expressions is the first algebra unit in the IGCSE Mathematics Higher scheme of work. It introduces important skills that students will use throughout the course, including expanding and factorising expressions.

Students learn to take out common factors, expand two and three brackets and collect like terms. They then use these skills in reverse to factorise quadratic expressions, including quadratics where the coefficient of (x2) is greater than 1.

What Success Looks Like

By the end of this unit students will be able to:

  • Factorise an expression by taking out the highest common factor, including powers.
  • Expand two brackets, and three binomials, then collect like terms.
  • Factorise a monic quadratic into two linear brackets.
  • Factorise a quadratic of the form ax2 + bx + c where a is not 1.

Prerequisite Knowledge

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

  • Collect like terms and expand a single bracket, including a negative factor.
  • Find the highest common factor of two integers, and use index laws to multiply and divide powers of the same base.
  • Write a monic quadratic as two brackets when the constant and the linear coefficient match, if that was met in earlier number work.

Key Mathematical Ideas

Take out the highest common factor

The factor outside the bracket is the largest number and the lowest power that divides every term. 6x3 − 9x2 is 3x2(2x − 3), not 3x(2x2 − 3x). Check by expanding.

Each term multiplies each term

For two brackets, four products appear, then the like terms are collected. A missing inner or outer product leaves the linear term wrong. For three binomials, expand two first, then multiply the quadratic by the third bracket.

A factor pair must add to the middle term

For x2 + bx + c, find two numbers that multiply to c and add to b. Expand to check before the brackets are declared. A pair that multiplies to c but does not add to b is not a factorisation.

When a is not 1, the pair shares a

For ax2 + bx + c, the numbers in the brackets must multiply to ac and still give the linear term when expanded. Factorising by grouping, or by trying pairs that include the factors of a, both work. Leaving a outside and factorising x2 + bx + c as if a were 1 does not.

Working Mathematically

Fluency

  • Factorise an expression with numerical and algebraic common factors, including powers.
  • Expand two linear brackets and collect the like terms.
  • Expand three binomials and write the cubic in descending powers.
  • Factorise a monic quadratic and a quadratic with a not equal to 1.

Reasoning

  • Explain why 2x is not the highest common factor of 6x3 and 9x2.
  • Show the four products from (x + 2)(x − 5) before collecting.
  • Check a proposed pair of brackets by expanding back to the quadratic.
  • Decide whether a quadratic is a difference of two squares before searching for a general pair.

Common Misconceptions with Algebraic Expressions

MisconceptionTeaching focus
Taking out a common factor that is not the highest power, so a power of x remains in every term inside.Ask which power of x divides every term. That lowest power, with the numerical HCF, goes outside.
Expanding two brackets as the product of the first terms plus the product of the last terms, and missing the two cross products.Write a two-by-two grid, or list first, outer, inner, last, then collect the middle pair.
When expanding three brackets, multiplying only the end terms of the third bracket by the quadratic.Expand the first pair fully. Then multiply every term of that quadratic by each term of the third bracket.
Choosing a factor pair that multiplies to c but does not add to b.Expand the proposed brackets before moving on. If the linear term is wrong, the pair is not a factorisation.
Factorising ax2 + bx + c by ignoring a, then tacking a on the front.The constants in the brackets must multiply to ac. Expand to check the coefficient of x2 as well as the constant.

Differentiation

Additional support

  • Begin common factors with integers only, then introduce a single power of x, then two letters.
  • Expand (x + a)(x + b) with both signs positive before a negative constant.
  • Start ax2 + bx + c with a equal to 2 and small integer pairs.

Additional challenge

  • Give a common-factor expression that includes a negative power or two variables.
  • Ask for the expansion of three brackets that already include a coefficient other than 1.
  • Offer a quadratic that needs a common numerical factor taken out before the two brackets are found.

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 five lessons, alongside the full Key Stage 3, GCSE, IGCSE and A-Level libraries.

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Algebraic Expressions Lessons


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