Q. 74.1( 140 Votes )

# Find the sum to n terms of the A.P., whose k^{th} term is 5k + 1.

Answer :

Let the first term be a and common difference be d.

Given that k^{th} term of the A.P. is 5k + 1.

k^{th} term = a_{k} = a + (k – 1)

∴ a + (k – 1)d = 5k + 1 ⇒ d k + (a - d) = 5k + 1

Comparing the coefficient of k, we obtain d = 5 and a – d = 1

⇒ a – 5 = 1

⇒ a = 6

Putting the value of a and d

∴

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