Q13 of 104 Page 457

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

2nd term = ar2-1 = ar1


5th term = ar5-1 = ar4


Dividing the 5th term using the 3rd term



r 3 = -


∴ r = -


∴ a = 1


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


n = 8 terms



⇒


⇒


∴


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