12^n = 3^n*2^2n
(3^n*2^2n-3^n)/(2^n+1) = {3^n(2^2n-1)}/(2^n+1) = {3^n (2^n-1) (2^n+1)}/ (2^n+1) = 3^n(2^n+1)
12^n = 3^n*2^2n
(3^n*2^2n-3^n)/(2^n+1) = {3^n(2^2n-1)}/(2^n+1) = {3^n (2^n-1) (2^n+1)}/ (2^n+1) = 3^n(2^n+1)