Question

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​

Answer 1

Answer:

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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