Binomial TheoremHard

Question

If the sum of the co-efficients in the expansion of (1 + 2x)n is 6561, then the greatest term in the expansion for x = 1/2 is :

Options

A.4th
B.5th
C.6th
D.none of these

Solution

3n = 6561 (put x = 1)
⇒ n = 8

⇒ 8 - r + 1 ≥ r ⇒ r ≤ ⇒ r = 4  (5th term is greatest)

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