I think in Ext 1 you only consider roots of multiplicity of 2. ie. If a is a double root of P(x) then P(a)=P'(a)=0. But in Ext 2 you can be asked roots of other multiplicity.
This was in our Year 11 preliminary exam for Ext 1. The question was something like, if a is a double root of P(x), then...