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 a × c
  • Add?to give b
  • Cheat by writing brackets as (ax + p)(ax + q) – Yes, I know! This is?not?correct!
  • Uncheat by cancelling common factors in each bracket