Saturday, May 28, 2016

discrete mathematics - Induction Proof: 2 divides n2+n for each ninmathbbN



So I am looking at some induction questions and I am trying to solve them on my own but I am getting stumped and frustrated. There was a previous question question that was answered, but I changed it to see if I could solve it. I am not getting that far.



How do I show by mathematical induction that 2 divides n2+n for all n belonging to the set of Natural Numbers. Here is what I have so far. Could I be pointed in the right direction? You can see below where I am stumped. This is where I am having the issue.




Basis: n=1,P(1) is true, 2 divides 12+1=2



Induction Hypothesis: 2 divides (k+1)2+(k+1) for some kZ1



Induction Step: (k+1)2+(k+1)=k3+3k2+3k+1=


Answer



Alright, so our inductive hypothesis is that k2+k is a multiple of 2 for some k. Then consider (k+1)2+(k+1)=k2+2k+1+k+1=(k2+k)+2k+2=(k2+k)+2(k+1).



By our inductive hypothesis, k2+k was an even number: because we are adding an even number, 2(k+1), to it, we still have an even number.




Therefore, (k+1)2+(k+1) must be even as well. This completes our proof.


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