Find the number of terms in the geometric series, 5+15+…+3645
2 answers
[(3645 - 5) / (15 - 5)] + 1
In a GP,
term(n) = a r^(n-1)
in yours, a = 5, r = 3
3645 = 5(3^(n-1) )
729 = 3^(n-1)
3^6 = 3^(n-1)
n-1 = 6
n = 7
There are 7 terms
in case you want the sum
sum(7) = a(r^7 - 1)/(r-1)
= 5(3^7 - 1)/2 = 5465
term(n) = a r^(n-1)
in yours, a = 5, r = 3
3645 = 5(3^(n-1) )
729 = 3^(n-1)
3^6 = 3^(n-1)
n-1 = 6
n = 7
There are 7 terms
in case you want the sum
sum(7) = a(r^7 - 1)/(r-1)
= 5(3^7 - 1)/2 = 5465