Hi guys, I'm totally new to number theory, so bear with me...

I'm only on page 2 of the textbook and am already stuck

To prove 1+2+3.... +n = n(n+1)/2, we are supposed to assume 1+2+3...+k = k(k+1)/2 for n<=k, and then add k+1 to both sides, etc. etc.

Okay, isn't that first assumption the very statement that we are trying to prove, except replacing n with k? Can someone enlighten me as to how this makes sense?