CSEC MATHEMATICS · MODULE 1 · LESSON A14

Factorising, Algebraic Fractions and the Laws of Indices

Common factors, grouping, difference of two squares, simplifying algebraic fractions with the four operations, and the laws of indices.

Fundamentals of Secondary Level MathematicsM1 5.7M1 5.8M1 5.9M1 5.13≈ 40 min🎮 3 games
Before you start

By the end of this lesson you can…

Step 1 · Watch

Explainer video

5 narrated scenes. Press play, listen and read along — the points appear as they are explained. Use ‹ Prev / Next › or the scene bar to jump to any scene.

LESSON A14 · EXPLAINER

Factorising, Algebraic Fractions and the Laws of Indices

Factorising is expanding in reverse — and it is the key that opens quadratic equations, algebraic fractions and half of Module 2.

Narration uses your device’s built-in voice. No sound? Switch to “Captions only” — the captions advance on their own.

Step 2 · Read

Key notes

Copy these into your notebook in your own words — that is how they stick.

Factorising order

1) common factor; 2) difference of two squares (2 terms); 3) grouping (4 terms); 4) quadratics (Module 2).

Difference of two squares

a² − b² = (a − b)(a + b). There is NO factorisation of a² + b² over the real numbers at this level.

Check

Expand your factors; you must return to the original expression.

Cancelling

Factorise first; cancel FACTORS (things multiplied), never terms.

Add / subtract fractions

Common denominator, then combine the numerators.

Multiply / divide fractions

Cancel across, multiply; divide by flipping.

Index laws

Multiply → add; divide → subtract; power of power → multiply; x⁰ = 1; x⁻ⁿ = 1/xⁿ.

Coefficients with powers

(2x³)² = 4x⁶: square the number too.

EXAM TIPS & COMMON MISTAKES

  • Always take out a common factor FIRST — even if you then see a difference of two squares.
  • In (2x³)² square the 2 as well: 4x⁶, not 2x⁶.
  • Cancel factors only: (x + 3)/3 does NOT simplify to x + 1.
  • Check every factorisation by expanding in your head or in the margin.
Play & practise

Games

3 quick games on this lesson. Earn XP and badges as you play — your best score for each game is saved. Games are for practice and do not change your exam readiness. More games in the Mathematics Arcade.

Step 3 · Practise

Paper 1 practice — multiple choice

8 items modelled on real CSEC Paper 1 questions. Choose one answer for each, then check. Aim for 80% or better. Work each item on paper first.

CSEC Paper 01 style · SO 5.13

1. 6x + 9 factorised completely is

Answer: A. Common factor 3: 3(2x + 3).
CSEC Paper 01 style · SO 5.13

2. x² − 49 factorises as

Answer: B. Difference of two squares.
CSEC Paper 01 style · SO 5.7

3. ax + ay + 2x + 2y factorises as

Answer: C. a(x + y) + 2(x + y) = (a + 2)(x + y).
CSEC Paper 01 style · SO 5.8

4. (x² − 9)/(x + 3) simplifies to

Answer: D. (x − 3)(x + 3)/(x + 3) = x − 3.
CSEC Paper 01 style · SO 5.8

5. x/3 + x/4 is equal to

Answer: A. (4x + 3x)/12 = 7x/12.
CSEC Paper 01 style · SO 5.9

6. a⁵ × a⁻² is equal to

Answer: B. Add the powers: 5 + (−2) = 3.
CSEC Paper 01 style · SO 5.9

7. (2x²)³ is equal to

Answer: C. 2³ × (x²)³ = 8x⁶.
CSEC Paper 01 style · SO 5.9

8. The value of 3⁻² is

Answer: D. 3⁻² = 1/3² = 1/9.
Step 4 · Apply

Paper 2 practice — structured questions

Write full answers, then reveal the mark scheme and tick the points you earned (17 marks in total). Show all your working — method marks count. Your answers are saved on this device.

CSEC Paper 02 style · Module 1 (Factorising)

Question 1 [9 marks]

Factorise each expression completely.

(a) 12ab − 18b² [2]

MARK SCHEME — (a) (max 2)

(b) 25x² − 4 [2]

MARK SCHEME — (b) (max 2)

(c) pq + 3p − 2q − 6 [3]

MARK SCHEME — (c) (max 3)

(d) Hence, or otherwise, simplify (25x² − 4)/(10x − 4). [2]

MARK SCHEME — (d) (max 2)

CSEC Paper 02 style · Module 1 (Indices and fractions)

Question 2 [8 marks]

Answer all parts.

(a) Simplify (3a²b)³ ÷ 9ab². [3]

MARK SCHEME — (a) (max 3)

(b) Evaluate 2⁻³ × 16^(1/2). [2]

MARK SCHEME — (b) (max 2)

(c) Express 2/(x + 1) + 3/(x − 2) as a single fraction. [3]

MARK SCHEME — (c) (max 3)

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Sources

Where this topic appears in CSEC papers

Find these in your own past-paper booklets for extra timed practice. Items above are written in the style of these papers; any adapted from a specific question say so.