What is the sum of the geometric sequence 1, 3, 9, … if there are 11 terms?

Question

10690 views around the world

You can reuse this answer
Creative Commons License

Answer 1 · 2016-01-21T18:13:33

#Sum=88573#

#a_2/a_1=3/1=3#

#a_3/a_2=9/3=3#

#implies# common ration#=r=3# and #a_1=1#

Number of terms#=n=11#

Sum of geometric series is given by

#Sum=(a(1-r^n))/(1-r)=(1(1-3^11))/(1-3)=(3^11-1)/(3-1)=(177147-1)/2=177146/2=88573#

#implies Sum=88573#