If 1/n is the sum of first n terms. then what is the product of 2014 terms…

2026

If 1/n is the sum of first n terms. then what is the product of 2014 terms (where 1! means 1 factorial ,2! means 2 factorial,.... n!.)

  1. A.

    1/(2013!2013!)

  2. B.

    1/(2013!2014!)

  3. C.

    -1/(2013!2013!)

  4. D.

    -1/(2013!2014!)

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Correct answer: D

Given the partial sums S_n = 1/n.

The nth term equals the difference of consecutive partial sums:

  • For n ≥ 2: t_n = S_n - S_{n-1} = 1/n - 1/(n-1) = -1/[n(n-1)].

  • For n = 1: t_1 = S_1 = 1.

Therefore the product of the first 2014 terms is

  • P = t_1 · ∏_{n=2}^{2014} t_n = 1 · ∏_{n=2}^{2014} ( -1/[n(n-1)] ) = (-1)^{2013} / ( ∏_{n=2}^{2014} n · ∏_{n=2}^{2014} (n-1) ).

  • Evaluate the products: ∏_{n=2}^{2014} n = 2014! and ∏_{n=2}^{2014} (n-1) = 2013!.

So P = (-1)^{2013}/(2014!·2013!) = -1/(2014!·2013!).

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