Question

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

Answer 1

As it is given that kth term of the AP = 5k + 1

∴ a_k = a + (k – 1)d

⇒ 5k + 1 = a + (k – 1)d

⇒ 5k + 1 = a + kd – d

Now, on comparing the coefficient of k, we get

d = 5

and a – d = 1

⇒ a – 5 = 1

⇒ a = 6

We know that,