Friday, 24 March 2017

elementary number theory - Prove that 7n+2 is divisible by 3 for all nmathbbN




Use mathematical induction to prove that 7n+2
is divisible by 3 for all nN.




I've tried to do it as follow.




If n=1 then 9/3=3.
Assume it is true when n=p. Therefore 7p+2=3k where kN. Consider now n=p+1. Then
7p+1+2=7p7+2=


I reached a dead end from here. If someone could help me in the direction of the next step it would be really helpful. Thanks in advance.


Answer



Hint




If 7n+2=3k then 7n+1+2=7(7n)+2=7(3k2)+2.


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