Q. 134.7( 7 Votes )

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

Answer :

2^{nd} term = ar^{2-1} = ar^{1}

5^{th} term = ar^{5-1} = ar^{4}

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

⇒

⇒

∴

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