Suppose the positive integer is n.
∴ n = 2q or n = 2q + 1 where q∈Z.
CASE 1:-
n = 2q
∴ n² - n = (2q)² - 2q
= 4q² - 2q
= 2(2q² - q)
CASE 2:-
n = 2q + 1
∴n² - n = (2q + 1)² - (2q + 1)
= 4q² + 4q + 1 - 2q - 1
= 4q² + 2q
= 2(2q² + q)
Thus, in any case, n² - n is divisible by 2.
Thus, n² - n is divisible by 2 for every positive integer n.