Question
The second term of an arithmetic sequence is 15 and the fifth term is -15. How many terms of this sequence will give you a sum of 0
Answers
oobleck
the two terms are three apart, so d = -10
The sequence is
25, 15, 5, -5, -15, -25, ...
The first 6 terms give a sum of zero.
If it weren't so obvious you could find n using
n/2 (2*25 - 10(n-1)) = 0
30n-5n^2 = 0
5n(6-n) = 0
n = 6
The sequence is
25, 15, 5, -5, -15, -25, ...
The first 6 terms give a sum of zero.
If it weren't so obvious you could find n using
n/2 (2*25 - 10(n-1)) = 0
30n-5n^2 = 0
5n(6-n) = 0
n = 6