S=1^2+2^2+3^2+....+ n^^2
S=1+ 2.(1+1) + 3.(2+1) +.....+ n(n-1 +1)
S=1 + 1.2 +2 + 2.3 + 3 +.......+ (n-1).n + n
S= (1 + 2 +3 +....+n) + (1.2 + 2.3 + 3.4 + ......+ (n-1)n )
S= n(n+1)2n(n+1)2 + n(n+1)(n−1)3n(n+1)(n−1)3
S= 3n(n+1)+2n(n+1)(n−1)63n(n+1)+2n(n+1)(n−1)6
S= n(n+1)(2n+1)6