if the sum of first 7terms of an ap is 49 and that of its first 17 terms is 289 find the sum of first n times of the AP
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Step-by-step explanation:a+(7-1)d=49
a+6d=49...(1)
a+(17-1)d=289
a+16d=289...(2)
(2)-(1), we get
10d=289-49
10d=240
d=24
Putting d in (1), we get
a+(24×6)=49
a+144=49
a=-95
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