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Let an be the nth term of an A.P. If Sn = a1 + a2 + a3 + + an = 700, a6 = 7 and S7 = 7, then an is equal to :
(4) 64
S7 = 72(a1 + a7) = 7a4 = 7 a4 = 1
a6 - a4 = 2d = 6 d = 3
a1 = a4 - 3d = 1 - 9 = -8
Sn = n2[2(-8) + (n-1)3] = n(3n - 19)2 = 700
3n2 - 19n - 1400 = 0 (n - 25)(3n + 56) = 0 n = 25
an = a25 = -8 + 24 3 = 64
Answer: (4)
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