Question

The nth term of an A.P. is (5n − 1). Find the sum of its ‘n’ terms.

Answer 1

a = 5(1) − 1

a = 5 − 1

a = 4

a_l = 5n − 1

`S_n = n/2(a + l)`

`S_n = n/2(4 + 5n − 1)`

`S_n = n/2(5n + 3)`