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KCET2008MathematicsSequences and Series

1 2 5 + 1 5 8 + equal to upto n terms is

Options

  1. An 4 n+6
  2. B1 6 n+4
  3. Cn 6 n+4
  4. Dn 3 n+7

Correct answer

C. n 6 n+4

Step-by-step solution

Let aligned S _ n &= 1 2 5 + 1 5 8 + 1 8 11 + + 1 (3 n-1)(3 n+2) &= 1 3 [ 1 2 - 1 5 + 1 5 - 1 8 + + 1 3 n-1 - 1 3 n+2 ] &= 1 3 [ 1 2 - 1 3 n+2 ] &= n 6 n+4 aligned

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