Q. 134.7( 7 Votes )
The 2nd and 5th terms of a GP are 
and 
respectively. Find the sum of n terms GP up to 8 terms.
Answer :
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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