Q. 74.1( 140 Votes )
Find the sum to n terms of the A.P., whose kth term is 5k + 1.
Let the first term be a and common difference be d.
Given that kth term of the A.P. is 5k + 1.
kth term = ak = 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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