Edexcel IGCSE Maths 復習筆記 2.4.1 Factorising Quadratics - Basics
Edexcel IGCSE Maths 復習筆記 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
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