If the nth term of an A.P. is 2n + 1, then the sum of first n terms of

1.	If the nth term of an A.P. is 2n + 1, then the sum of first n terms of the A.P. is A. n (n – 2) B. n (n + 2) C. n (n + 1)D. n (n –1)
Answer» a_n= a + (n–1) d = 2n + 1 (given)…………(1) S_n= n/2 (2a + (n–1) d) By putting n=1 in (1) a=3 similarly a₂= 5 a₃= 7 d= common difference = a₂ – a₁ = 2S_n = n/2 (6 + (n–1) 2) = n/2 (2n + 4) = n (n + 2)

If the nth term of an A.P. is 2n + 1, then the sum of first n terms of the A.P. is A. n (n – 2) B. n (n + 2) C. n (n + 1)D. n (n –1)

Answer»

a_n= a + (n–1) d = 2n + 1 (given)…………(1)

S_n= n/2 (2a + (n–1) d)

By putting n=1 in (1)

a=3

similarly a₂= 5

a₃= 7

d= common difference = a₂ – a₁

= 2S_n = n/2 (6 + (n–1) 2)

= n/2 (2n + 4)

= n (n + 2)