In the normal mathematical induction you are assuming the statement P is true for some value, say k, that is P(k) is true. Then you try to manipulate P(k+1) to something that will use P(k). That is, when considering P(k+1), you are falling back to P(k). In strong mathematical induction you are assuming that the statement is true for all values up to k. This is useful in cases where you don't know which value you are going to have to fall back on. Since you have been told to use strong mathematical induction, assume that the statement is true for all integer powers up to and including "n". Then consider n+1 and try to fall back on an arbitrary, small case.