® An arithmetic progression (A.P.) is a sequence in which terms increase or decrease regularly by the same constant. This constant is called common difference of the A.P. Usually, we denote the first term of A.P. by a , the common difference by d and the last term by l .
The general term or the n th term of the A.P. is given by a n = a + ( n – ) d . The sum S n of the first n terms of an A.P. is given by S 2a+ n – d = a+l