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Can the cube of an integer end with one 1? Can it end with 2 ones? three 1's? (Experiment) We can show by induction that there always exists a number ending in k 1's. But there exists (prove this!) B with 0<=B<10 such that 3B ends in A. Show that [B*10k-1 + N]3 ends in k 1's. Hint: binomial expansion. Bonus question: why does this NOT work for squares? What is the next power it does work for? Good Hunting! | ||||||||||||
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Math Central is supported by the University of Regina and The Pacific Institute for the Mathematical Sciences. |