Solution :
Given a14=2a8;a6=−8
an=a+(n−1)d
∴a+13d=2(a+2d)
a+13d=2a+14d
a=−d----------(1)
a+rd=−8
substituting for d we get,
−d+5d=−8
4d=−8
d=−2
∴a=2
sn=n2[2a+(n−1)d
S2n=2n2[2(2)+(19)(−2)]
=10[4−38]
=−340
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Answers & Comments
Verified answer
A+ 13 d = 2(a+7d)a + 13d = 2a + 14d
-a -d = 0
a+ d = 0 = a2 ---- --------> 1
a + 5d = -8 -----> 2
2-1
a + 5d = -8
a +. d = 0
------------------
a = 2
D = -2
a 20 = 2+ 19*-2
= -36
S20 = 10(2+(-36))
= -340
Hope it's helpful.
All the best.
Solution :
Given a14=2a8;a6=−8
an=a+(n−1)d
∴a+13d=2(a+2d)
a+13d=2a+14d
a=−d----------(1)
a+rd=−8
substituting for d we get,
−d+5d=−8
4d=−8
d=−2
∴a=2
sn=n2[2a+(n−1)d
S2n=2n2[2(2)+(19)(−2)]
=10[4−38]
=−340