Find the sum of 15 terms of the arithmetic series 25+19 + … .
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Answer:S15= -255
Step-by-step explanation:
Sn=n/2[2a+(n-1)d]
= 15/2[2×25+(15-1)×-6]
=15/2[50+14×-6]
=15/2[50-84]
=15/2×-34
=15×-17
=-255
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