SOLUTION: The sum of an arithmetic series is 1356 and the first term is -1. If the common difference is 5, how many terms are in the sequence?
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Question 336261: The sum of an arithmetic series is 1356 and the first term is -1. If the common difference is 5, how many terms are in the sequence?
Answer by jrfrunner(365) (Show Source): You can put this solution on YOUR website!
arithmetic series: +...+ summed from i=1 to n
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Given , diff=5 and sum=1356
(multiply both sides by 2)
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using quadratic solution
with a=5, b=-7, c=-2712
or
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since we need the solution to be positive, the first solution is not needed
and n=24
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