What is the sum of the geometric sequence -3 18 -108.... If there are 8 terms?

1 Answer
Apr 7, 2018

#S_8=719835#

Explanation:

To find the sum of the first #S_n# terms of a geometric sequence, use the formula #S_n=(a(1-r^n))/(1-r)# where #n# is the number of terms #a# is the first term and #r# is the common ratio.

#a=-3, r=-6 and n=8#

#S_8=((-3)(1-(-6)^8))/(1-(-6))#

#S_8=((-3)(1-1679616))/(7)#

#S_8=((-3)(-1679615))/(7)#

#S_8=719835#