Edexcel IGCSE Maths

Revision Notes

2.4.1 Factorising Quadratics - Basics

What is a quadratic expression?

  • A quadratic expression looks like this:
    ax2 + bx + c (as long as a ≠ 0)
  • Note: If there are any higher powers of x (like x3 say) then it is not a quadratic!

Factorising a 3-term quadratic expression (a = 1)

  • Signs in quadratic determine signs in brackets:
    • if c is positive then both signs are the same as the sign of b
    • if c is negative then the signs are different and bigger number has the sign of b
  • Using those signs find numbers p and q which
    • multiply to give c
    • add to give b
  • Write down the brackets (x + p)(x + q) – that’s your answer!
    Don’t forget – both p and q here can be negative!

Exam Tip

Make sure you know if you are being asked to:

  • Solve an equation (look for the “=”) or
  • Factorise an expression (no “=”)

Do not confuse the two things.

When the quadratic expression only has two terms check for:

  • Simple factorisation (no number term, ie. when c = 0 )
  • Difference Of Two Squares (no x term, ie. when b = 0)

Worked Example

Factorising Quadratics - Simple Worked Example, downloadable IGCSE & GCSE Maths revision notes


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