How to factorise a quadratic when the leading coefficient is 1, how the AC method handles the case when it is not, and a short proof of why splitting the middle term always works.
- algebra
- quadratics
- factorising
Problems and proofs
Worked problems and methods, written up properly — including why each one actually works, not just how to do it.
Multiplying by 11 and 12 in your head using Trachtenberg's rules — and the place-value argument that shows exactly why the rules work.
- arithmetic
- mental Maths
- place value