Question

( sum_{k=1}^{infty} t^{2}=1- )
( 2 quad n z )
( (n-1)(n-1+2)(2(n-1)+1) )
( frac{6}{2}+frac{(n+1)(n) times 3}{2 times j} )
( frac{(n-1)(n)}{6}+frac{(2 n-1)}{6} )
( =frac{n(n-1)}{6}[2 n-1+3] )
( =frac{n(n-1)}{6}(2 n+n)=frac{n(n-1)(n+1)}{3} )

# n-1 - n(n-1) (n+1) Prove that t(t+1) = - ?, for all natural numbers n 2 2. t=1

Solution