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Find the sum to n terms of the A.P., whose kth term is 5k + 1.

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Solution:

As, it is given that   k   th   term of the A.P.  is 5k   + 1.

therefore,

  ak   =   a   + (k   – 1)d

⇒   a   + (k   – 1)d   = 5k   + 1

⇒ a   +   kd   –   d   = 5k   + 1

now, on comparing the coefficient of   k, we get,

d = 5

and 

 a   –   d   = 1

⇒   a   – 5 = 1

⇒   a   = 6

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