Question #768a8

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Answer 1 · 2017-10-26T01:01:54

First term a_1 = 39.5554

# n^(th)term = a r^(n-1)# for a geometric sequence where a is the first term and r is the common ratio.

# 3^(rd) term = a r^2 = 81# (1)

#6^(th) term = a r^5 = 237.375# (2)

Dividing (2) by (1),

#r^3 = 237.375/81 = 2.9306#

# r = (2.9306)^(1/3) = 1.431#

Substituting value of r in (1),

#a * (1.431)^2 = 81#

#:. a = 81 / (1.431)^2 = 39.5554#