prove by mathematical induction, that for n

$\displaystyle \sum_{i=1}^n i^2 = \frac{1}{6}n(n+1)(2n+1) $

assume that the summation formula is true for n=k

$\displaystyle \sum_{i=1}^n i^{2} = \frac{1}{6} k (k+1) (2k+1) $

so must be true for n= k+1 ?

so do I put k+1 into the formula, and try and get it match the original? really stuck from this part,