InterviewSolution
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InterviewSolution
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If | x | < 1, then the coefficient of xn in the expansion of (1 + x + x2 + x3 + .....)2 is (a) n – 1 (b) n (c) n + 1 (d) n + 2 |
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Answer» Answer : (c) n+1 (1 + x + x2 + x3 + .....)2 = {(1 – x) –1)}2 = (1 – x) –2 = 1 + 2x + 3x2 + 4x3 + ..... + (n + 1)xn + ..... ∴ Coefficient of xn in this expansion = (n + 1). |
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