Edexcel IGCSE Maths 复习笔记 2.4.4 Factorising Quadratics - General
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!
Does it factorise?
- It is sensible to check before trying to factorise a quadratic that it actually does factorise!
- A quadratic will factorise if (and only if) the discriminant (b2 – 4ac) is a perfect square
- If it does factorise then you have to decide what to do:
- Always check for a Common (numerical) Factor before you factorise – spotting it early will make life a lot easier
- Take it out and just leave it in front of a big bracket
- 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)
- Once you have decided that it is a factorisable three term quadratic with no common numerical factors then you can follow the normal rules (see other Notes for those!)