(2n^-1)(n+1)-(n^+1)(2n-1)=

( 2n^2 - 1)(n + 1) - ( n^2 + 1)(2n - 1) = 2n^3 + 2n^2 - n - 1 - - ( 2n^3 - n^2 + 2n - 1) = 2n^3+2n^2-n-1-2n^3+n^2-2n+1 = = 3n^2- 3n = 3n(n - 1)