The first term on the left of the equation is the last term of the previous equation plus 1, and the last term is equal to the square of n (n is the number of formulas).
This is actually an arithmetic series: on the left.
[(n- 1)^2+ 1]+...+n^2=( 1/2)*([(n- 1)^2+ 1]+n^2)*(2n- 1)
= (N2-n+1) * (2n-1) = n3+(n-1) 3 = right.