How many terms of the series -3 -1 + 1 +….. add up to 165?
Explanation
Observe that the common difference = 2, substitute to get 165 = (frac{n}{2})[2(-3) + (n – 1)2]
n(^2) – 4n – 165 = 0
n = 15 or n = -11
Therefore, the number of terms is 15 as n cannot be negative.