The 2^nd and 5^th terms of a GP are and respectively. Find the sum of n terms GP up to 8 terms.

2^nd term = ar^2-1 = ar¹

5^th term = ar^5-1 = ar⁴

Dividing the 5^th term using the 3^rd term

r ³ = -

∴ r = -

∴ a = 1

Sum of a G.P. series is represented by the formula, , when |r|<1. ‘S_n’ represents the sum of the G.P. series upto n^th terms, ‘a’ represents the first term, ‘r’ represents the common ratio and ‘n’ represents the number of terms.

n = 8 terms

⇒

⇒

∴