How many terms of G.P. 3, 3², 3³,... are needed to give the sum 120? (Show Your Work)! (90 Points) Please Help!
Mathematics · College · Thu Feb 04 2021
llm
Answered on
In the given GP , first term = 3, common ratio is 3
sum is 120
formula for sum in GP is --
(a(r^n-1)/(r-1)
Here a = first term, r = common ratio
putting the values ,
(3(3^n-1)/(3-1)=120
3((3^n)-1 )/2 = 120
3^n -1 = 80
3^n = 81
therefore , n = 4 is answer
since 3^4 = 81
4 terms are required