Answer:
k = 10
Step-by-step explanation:
The sum of k terms of a geometric sequence with first term a1 and common ratio r is given by ...
... Sk = a1·(1 -r^k)/(1 -r)
For the given numbers, this is ...
... 118096 = 78732·(1 -(1/3)^k)/(1 -1/3)
Manipulating this to get the term containing k, we have
... 1 -(2/3)(118096/78732) = (1/3)^k
... 1/59049 = (1/3)^k
Taking logarithms, we get
... -log(59049) = -k·log(3)
... log(59049)/log(3) = k = 10
