Submitted by Anonymous (not verified) on
Forums:
In question 1 (iv), in the mark scheme 5 marks are allocated for this. Is any counter example required for the full 5 marks (i.e select any a,b,c that fit the original conditions and show S2S7=/=S9).
The mark scheme seems to imply that a proof is required (ie. that r=/= 0). However the question does not actually appear to ask this (by the words proof OR counterexample).
You are right - the mark
Submitted by stcs on
You are right - the mark scheme doesn't quite match the question. I'm sure that it would have been changed for the actual examination (I don't have a copy of the final mark scheme).
It seems to me that the marks should be given either for the proof that the relation does not hold in general or for a counterexample showing that it does not work in a specific case. Nearly always, it is easiest to find a simple counter-example - and actually, in this case, it is best to find a counter-example since that is what the question asks for.
It seems to me that 5 marks is rather a lot for this part of the question but that might have changed as well in the final version (by which time the principal examiner would have looked through 100 scripts and modified the mark scheme accordingly).
Stephen