The general form of an AP is a , a+d, a+2d,.....
Which of the following series forms an AP?
(i)a–2d,a–d,a,a+d,a+2d
(ii)a,a+d,a+2d,a+3d,a+4d
(iii)a–3d,a–d,a+d,a+3d
Identify the common difference of the given AP: a, a+d, a+2d, a+3d, ...