If r = 3 and the sum of 6 terms of the geometric series is 3640, what is the first term?

1 Answer
May 7, 2016

Answer:

First term is #10#

Explanation:

In a geometric series, if #a# is the first term and ratio between a term and its preceding term is #r#, then sum of first #n# terms ia given by

#a(r^n-1)/(r-1)#

As #r=3# and sum of first #6# terms is #3640#, we have

#a(3^6-1)/(3-1)=3640#

hence #a(729-1)/(3-1)=(axx728)/2=3640#

or #364a=3640# and hence

#a=10#.