Hey everyone, I know this is probably basic for you but I really can't understand this.

This is the lesson I've been following.

Factoring Quadratic Trinomials by MATHguide

I have learned to Factorise the Quadratic Equations which is (Factoring on that website, I think thats pretty easy, But for some reason I really dont understand the next part which is (Factoring )

I think I understand what it's trying to get to, but I just can't get my head around it.

Does anyone have any easier or alternative ways of understanding this ?

Thanks.