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What is the Fourth term of an AP of n terms whose sum is n ( n +1) ?

Options

  1. A6
  2. B8
  3. C12
  4. D20

Correct answer

B. 8

Step-by-step solution

Given, sum of n terms (S_n )=n(n+1) We know, T _ n = S _ n - S _ n -1 aligned & =[ n ( n +1)]-[( n -1)( n -1+1)] & = n ( n +1)-( n -1) n & = n ( n +1- n +1) & =2 n & Fourth term, T ₄=2(4)=8 aligned

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