Year 10 - Factorising by common factor - Free practice

Year 10 Factorising by Taking Out a Common Factor Worksheets & Practice

Spot the common factor, write the brackets, check your answer. Worked solutions every time, free.

Quick answer

How do you factorise an expression by taking out a common factor?

Find the highest common factor (HCF) of all terms, then divide each term by it and write the result in brackets. For example, 6x² + 9x has HCF 3x, so it factorises to 3x(2x + 3). Check by expanding: the brackets should reproduce the original expression.

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Six questions across Foundation, Standard and Extension, with full worked solutions, written to the Australian Curriculum.

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Worked examples

Year 10 factorising by common factor: worked examples

Three examples, from a standard question to a worded problem. Have a go at each one before you open the solution.

  1. Example 1 · Factorising with a numerical and single-variable common factor

    Factorise 6x3+9x2−3x6x^3 + 9x^2 - 3x.

    Show worked solution

    Key idea: Find the HCF of all terms, write it outside the brackets, then divide each term by the HCF to find what goes inside.

    1. Find the HCF of the coefficients 66, 99 and 33: the HCF is 33.
    2. Find the HCF of x3x^3, x2x^2 and xx: the lowest power is x1=xx^1 = x.
    3. So the overall HCF is 3x3x.
    4. Divide each term by 3x3x: 6x33x=2x2,9x23x=3x,−3x3x=−1\frac{6x^3}{3x} = 2x^2, \frac{9x^2}{3x} = 3x, \frac{-3x}{3x} = -1
    5. Write the factorised form: 6x3+9x2−3x=3x(2x2+3x−1)6x^3 + 9x^2 - 3x = 3x(2x^2 + 3x - 1)

    Check: 3x(2x2+3x−1)=6x3+9x2−3x3x(2x^2 + 3x - 1) = 6x^3 + 9x^2 - 3x ✓

    Answer: 3x(2x2+3x−1)3x(2x^2 + 3x - 1)

  2. Example 2 · Factorising with a multi-variable algebraic common factor and a negative

    Factorise −12a3b2+8a2b3−4a2b-12a^3b^2 + 8a^2b^3 - 4a^2b.

    Show worked solution

    Key idea: When the leading term is negative, take out a negative common factor so the first term inside the brackets is positive. Find the full HCF including all variables.

    1. Find the HCF of the coefficients 1212, 88 and 44: the HCF is 44.
    2. Include the negative sign: take out −4-4.
    3. Find the HCF of the variable parts: lowest power of aa is a2a^2; lowest power of bb is b1=bb^1 = b. So the variable HCF is a2ba^2b.
    4. Overall factor to take out: −4a2b-4a^2b.
    5. Divide each term by −4a2b-4a^2b: −12a3b2−4a2b=3ab,8a2b3−4a2b=−2b2,−4a2b−4a2b=1\frac{-12a^3b^2}{-4a^2b} = 3ab, \frac{8a^2b^3}{-4a^2b} = -2b^2, \frac{-4a^2b}{-4a^2b} = 1
    6. Write the factorised form: −12a3b2+8a2b3−4a2b=−4a2b(3ab−2b2+1)-12a^3b^2 + 8a^2b^3 - 4a^2b = -4a^2b(3ab - 2b^2 + 1)

    Check: −4a2b(3ab−2b2+1)=−12a3b2+8a2b3−4a2b-4a^2b(3ab - 2b^2 + 1) = -12a^3b^2 + 8a^2b^3 - 4a^2b ✓

    Answer: −4a2b(3ab−2b2+1)-4a^2b(3ab - 2b^2 + 1)

  3. Example 3 · Factorising with a binomial common factor

    A rectangular garden bed has an area that can be expressed as 5x(x+3)−2(x+3)5x(x+3) - 2(x+3) square metres, where xx is a positive number. Write the area as a product of two factors, and find the area when x=4x = 4.

    Show worked solution

    Key idea: When the same bracket appears in every term, the whole bracket is a common factor and can be taken out just like a single term.

    1. Identify the common binomial factor: (x+3)(x + 3) appears in both terms.
    2. Take out (x+3)(x + 3): 5x(x+3)−2(x+3)=(x+3)(5x−2)5x(x+3) - 2(x+3) = (x+3)(5x-2)
    3. Check by expanding: (x+3)(5x−2)=5x2−2x+15x−6=5x2+13x−6(x+3)(5x-2) = 5x^2 - 2x + 15x - 6 = 5x^2 + 13x - 6, and 5x(x+3)−2(x+3)=5x2+15x−2x−6=5x2+13x−65x(x+3) - 2(x+3) = 5x^2 + 15x - 2x - 6 = 5x^2 + 13x - 6 ✓
    4. Substitute x=4x = 4: Area=(4+3)(5×4−2)=7×18=126 square metres\text{Area} = (4+3)(5 \times 4 - 2) = 7 \times 18 = 126 \text{ square metres}

    Answer: (x+3)(5x−2)(x+3)(5x-2); the area when x=4x = 4 is 126126 square metres.

Common mistakes

Where students usually lose marks

Only taking out a partial common factor

HCF of 6x3+9x2−3x6x^3 + 9x^2 - 3x taken as 33 instead of 3x3x, giving 3(2x3+3x2−x)3(2x^3 + 3x^2 - x).

Always look for the HCF of both the coefficients and the variable parts. Check that nothing inside the brackets still shares a factor with the one you took out.

Sign errors when taking out a negative factor

−4a2b(3ab−2b2+1)-4a^2b(3ab - 2b^2 + 1) written incorrectly as −4a2b(3ab+2b2−1)-4a^2b(3ab + 2b^2 - 1) after dividing 8a2b38a^2b^3 by −4a2b-4a^2b.

When you divide a positive term by a negative factor the result is negative, and vice versa. After factorising, always expand your answer to check every sign matches the original expression.

Forgetting the +1 (or -1) when a whole term is taken out

3x(2x2+3x)3x(2x^2 + 3x) written for 6x3+9x2−3x6x^3 + 9x^2 - 3x, dropping the −3x-3x term entirely.

Every term in the original expression must appear inside the brackets. When a term equals the HCF exactly, dividing it by the HCF gives 11 (or −1-1), which must be written inside the brackets.

Treating a binomial factor as two separate factors

5x(x+3)−2(x+3)5x(x+3) - 2(x+3) rewritten as (5x−2)(x)(3)(5x-2)(x)(3) by splitting the bracket (x+3)(x+3) apart.

Treat the entire bracket (x+3)(x+3) as a single unit, just like a pronumeral. Take it out as one factor: (x+3)(5x−2)(x+3)(5x-2).

Try one yourself

Your turn

Factorise 12a3−8a212a^3 - 8a^2 by taking out the highest common factor. Enter your answer as an expression.

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About this worksheet

Why we built it

Factorising by taking out a common factor is the essential first step in almost every algebraic factorising problem in Year 10. These worksheets build the skill from numerical common factors through to algebraic ones, including expressions where the common factor is itself a binomial, with full worked solutions so students can see exactly where their thinking needs to shift.

What's covered

Sub-skills your student will practise

  • ✓Identifying the highest common factor (HCF) of terms
  • ✓Factorising expressions with numerical common factors
  • ✓Factorising with single-variable algebraic common factors
  • ✓Factorising with multi-variable algebraic common factors
  • ✓Taking out a negative common factor
  • ✓Factorising when the common factor is a binomial expression

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Frequently asked

Questions parents ask about factorising by common factor

What does 'taking out a common factor' actually mean?

It means rewriting an expression as a product by dividing every term by the highest common factor and placing that factor outside a pair of brackets. For example, 6x² + 9x becomes 3x(2x + 3).

How do students find the highest common factor of algebraic terms?

Find the HCF of the coefficients first, then include any variables that appear in every term, using the lowest power of each. For 4x³ and 6x², the HCF is 2x².

Why do teachers ask students to 'check by expanding'?

Expanding the brackets after factorising multiplies everything back out, so the result should match the original expression exactly. It is a quick, reliable way to catch errors in the factorised form.

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