GCSE Further Maths · Topic guide

Algebraic Fractions: Simplifying, Multiplying and Dividing

An algebraic fraction is a fraction whose numerator or denominator contains algebraic expressions, such as (x + 3)/(x^2 - 9). Simplifying one means factorising the numerator and denominator fully and cancelling any common factor, while multiplying and dividing algebraic fractions follows the same rules as multiplying and dividing ordinary numerical fractions. This is a core AQA Further Maths skill.

Grade 7-9 (Level 2)AlgebraAQA Level 2

Before you start

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Method

  1. Factorise the numerator and denominator of each fraction fully, using common factors, the difference of two squares or quadratic factorising as needed.
  2. Cancel any factor that appears in both the numerator and denominator; never cancel individual terms that are not full factors.
  3. When multiplying two fractions, factorise both fractions first, then cancel common factors across the whole calculation before multiplying what remains.
  4. When dividing by a fraction, turn the second fraction upside down (find its reciprocal) and multiply instead.
  5. Multiply the remaining numerators together and the remaining denominators together to leave a single fraction.
  6. Check the final fraction cannot be simplified any further before writing your answer.

Worked example

Simplify fully (x^2 + x - 6)/(x^2 - 9).

  1. Factorise the numerator: x^2 + x - 6 = (x + 3)(x - 2).
  2. Factorise the denominator using the difference of two squares: x^2 - 9 = (x - 3)(x + 3).
  3. Rewrite the fraction as [(x + 3)(x - 2)] / [(x - 3)(x + 3)].
  4. Cancel the common factor of (x + 3) from the numerator and denominator.
  5. Final answer: (x - 2)/(x - 3).

Practice questions

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Q1Simplify fully (6x^2y)/(9xy^3).Show answer

Answer: 2x/(3y^2) (divide the coefficients by 3 and cancel matching powers of x and y)

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Q2Simplify fully (3x + 12)/(x^2 + 4x).Show answer

Answer: 3/x (factorise to 3(x+4)/[x(x+4)] and cancel (x+4))

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Q3Simplify fully (x^2 - 25)/(x^2 + 2x - 15).Show answer

Answer: (x - 5)/(x - 3) (cancel the shared factor (x+5))

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Q4Simplify fully (2x/(5y)) x (15y^2/(4x^2)).Show answer

Answer: 3y/(2x) (multiply then simplify the numerical coefficient to 3/2)

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Q5Simplify fully [(x^2 - 9)/(x + 4)] / [(x - 3)/(2x + 8)].Show answer

Answer: 2x + 6, or 2(x + 3) (invert and cancel (x+4) and (x-3))

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Q6Simplify fully [(x^2 + 6x + 8)/(x^2 - 16)] x [(x^2 - 4x)/(x^2 + 5x + 6)].Show answer

Answer: x/(x + 3) (cancel (x+2), (x+4) and (x-4))

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Exam-style questions

Written in the style of a GCSE Further Maths exam paper, with a full mark scheme.

Q1[3 marks]

Simplify fully (4x - 28)/(x^2 - 7x).

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Q2[4 marks]

Simplify fully (x^2 - 36)/(x^2 + x - 30).

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Q3[5 marks]

A rectangular tile has area (x^2 - 16)/(x + 2) cm^2 and length (x - 4)/(x^2 - 4) cm. Find an expression for the width of the tile in its simplest form.

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See real GCSE Further Maths past-paper questions, with official mark schemes

Free printable worksheet

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