This has to do with positive integers.

I'm stating that since k^2-1 is even, then 2 must divide it, so by the definition:

k^2 -1 = 2c , for some integer c.

Then i figures since k^2 -1 is (k+1)(k-1) that I could use this. The only problem is that I end up with

k-1 = 2*(c/k+1) , which doesn't work because of the fraction.

I am also confused because of the OR in the statement I am trying to prove.