How many terms of the series -3 -1 + 1 +..... add up to 165?
FURTHER MATHEMATICS
WAEC 2019
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.
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