prove that (3x+1)^2 - (3x-1)^2 is a multiple of 4 for all positive integer values of x
(3x + 1)2 = 9x2 + 6x + 1 (3x - 1)2 = 9x2 - 6x + 1 (9x2 + 6x + 1) - (9x2 - 6x + 1) = 12x 12x/4 = 3x Therefore for all positive integers of x the result is a multiple of 4
