Hello!

I'm having trouble proving this relation:

$\displaystyle 1^2+3^2+5^2+...(2n+1)^2=\frac{(n+1)(2n+1)(2n+3)}{3 }$

It's implied that I should use that:

$\displaystyle 1^2+2^2+3^2+...+k^2=\frac{k(k+1)(2k+1)}{6}$

I've tried substituting k=(2n+1) in the second formula, but it's not working. I can't really see why it isn't...

Could someone lead me in the right direction here?