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The maximum sum of the series is
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a
310
b
290
c
320
d
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Correct option is A
The given series is arithmetic whose first term = 20, common difference = – . As the common difference is negative, the terms will become negative after some stage. So the sum is maximum if only positive terms are added.Now, tn=20+(n−1)−23≥0 if 60−2(n−1)≥0 or 62≥2n or 31≥n∴ The first 31 terms are non-negative.∴ maximum sum=S31=3122×20+(31−1)−23=312(40−20)−310Similar Questions
If the sum of first terms of an is , then the sum of squares of these terms is
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