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If S_ n = 1 6 11 + 1 11 16 + 1 16 21 + to n terms, then 6 S_ n =

Options

  1. A1 (5 n+6)
  2. B(2 n-1) 5 n+6
  3. Cn (5 n+6)
  4. D5 n-4 5 n+6

Correct answer

C. n (5 n+6)

Step-by-step solution

We have, S_ n = 1 6 11 + 1 11 16 + 1 16 21 + +n terms = 1 5 ( 1 6 - 1 11 + 1 11 - 1 16 + 1 5 n-1 - 1 5 n+6 )= 1 5 ( 1 6 - 1 5 n+6 )= 1 5 [ 5 n+6-6 6(5 n+6) ]= 1 5 [ 5 n 6(5 n+6) ] So, 6 ~S _ n = n (5 n+6)

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