Question

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

Answer 1

It is given that the kth term of the A.P. is 5k + 1.
kth term = ak = a + (k – 1)d
∴a + (k – 1)d = 5k + 1 a + kd – d = 5k + 1
∴Comparing the coefficient of k, we obtain d = 5 a – d = 1
⇒ a – 5 = 1
⇒ a = 6