Let be an odd prime number and be integers so that the integers
are all divisible by . Prove that divides each of , and .
Solutions — 3
Solution 1
Set . If one of is divisible by , then all of them are. Indeed, for example, if , then implies , and then implies . The other cases follow similarly.
So for the sake of contradiction assume none of is divisible by . Then
and
So . But then
which forces . Thus
implying , a contradiction. Thus the proof is complete. □
Solution 2
As before, we may assume divides none of , and and set . Then
and multiplying these three equations yields . By cancelling the factor , we get . Now
so
so either or . In the latter case, so or . In any case, two out of are the same mod , so one of the equations gives where and , hence odd implies so , the desired contradiction. □
Solution 3
We have
Thus,
Thus, and hence since is odd. Now, finish as before. □
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