Case 2. Suppose next that a and b are both odd and thus gcd(a + b, a − b) = 2. Therefore gcd((a + b)/2, (a − b)/2) = 1. Rewrite (2) as ((a − b)/2)z = ((a +b)/2)y. A similar argument now produces x = ka(a + b)/2, y = kb(a − b)/2, z = kb(a + b)/2, and w = ka(a − b)/2. Hence n = xy = wz = k2ab(a2 − b2)/4.