The 14th term of an ap is twice its 8th term if the 6th term is minus 8 then find the sum of its first 20 terms
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Answer:
Given,
a6 =−8
a+(6−1)d=−8
a+5d=−8
a=−8−5d
T
14
=2T
8
a+13d=2(a+7d)
a+13d=2a+14d
a=−d
−8−5d=−d
−8=4d
d=−2
a=2
s
20
=
10
20
(2+2+(20−1)(−2))
=10(4+19(−2))
=10(4−38)
=−340
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