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MHT CET2019Evening ShiftMathematicsSequences and SeriesActual

If ∑ r = 1 n 2 r + 1 = 440 , then n =…..

Options

  1. A20
  2. B22
  3. C21
  4. D19

Correct answer

A. 20

Step-by-step solution

We have, ∑ r = 1 n 2 r + l = 440 ⇒ 3 + 5 + 7 … + 2 n + 1 = 440 ⇒ n 2 2 × 3 + n - 1 2 = 440 ⇒ n 3 + n - 1 = 440 ⇒ n n + 2 = 440 ⇒ n = 20

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