the sum of first 7 terms of an AP is 49 and that of first 17 terms is 289, find the sum of first n terms
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Answered by
1
a+6d=49____1
a+16d=289___2
(2)-(1)
a+6d-a-16d=49-289
-10d=-240
d=24
a+6×24=49
a=49-146
a=-97
an=a+(n-1)d
a+16d=289___2
(2)-(1)
a+6d-a-16d=49-289
-10d=-240
d=24
a+6×24=49
a=49-146
a=-97
an=a+(n-1)d
SouravRonald:
in your solution .. you have assumed the 7th term as 49.. while.. it is the sum of 6 terms is 49
*7 terms is 49
because in AP a7 =a+6d
Answered by
0
after solving.. we get a=1 and d=2.. So the answer is .. n/2(2+(n-1)2)
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