Binomial TheoremHard

Question

If |x| < 1, then the co-efficient of xn in the expansion of (1 + x + x2 + x3 +....)2 is

Options

A.n
B.n - 1
C.n + 2
D.n + 1

Solution

Co-efficient of xn in (1 - x)- 2 = 2 + n -1 C1 = n + 1

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