® The arithmetic mean A of any two numbers a and b is given by

® The arithmetic mean A of any two numbers a and b is given by a+b i.e., the sequence a , A, b is in A.P. ® A sequence is said to be a geometric progression or G.P. , if the ratio of any term to its preceding term is same throughout. This constant factor is called the common ratio . Usually, we denote the first term of a G.P. by a and its common ratio by r . The general or the n th term of G.P. is given by a n = ar n – . The sum S n of the first n terms of G.P. is given by MATHEMATICS – – S – a r or , if r r – ≠