sorry didn't mean to send it ...

So next step -- Proof by Induction I have Assume the Assertion is true for n = K .. and show that if follows the assumption that the assertion is true for n = K +1 what i am lost on is where we get

1 + 2 + 3 ....+(K+1) = (K+1) (K+2) / 2 than what does it go to??