given a=7,a13=35, Find d and Sn
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Answer:
a = 7
a13 = 35
=> a + (n - 1)d = 35
=> 7 + (13 - 1)d = 35
=> 7 + 12d = 35
=> 12d = 35 - 7
=> 12d = 28
=> d = 28/12
=> d = 7/3
Sn = n/2{2a + (n - 1)d}
S13 = 13/2{2 × 7 + (13 - 1)7/3}
= 13/2{14 + 12 × 7/3}
= 13/2 {14 + 4 × 7}
= 13/2{14 + 28}
= 13 × 42
__
2
= 13 × 21
= 273
Ans. d = 7/3, Sn = 273
Hope it helps.
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