Question

The suitable formula to find the sum of first n terms of the AP 1 + 3 + 5 + 7 + ------ is ______
(a) 2 n² (b) n(n + 1 ) (c) n² (d) n(n-1)

Answer 1

Sn = n/2(2a+(n-1)d)

Here a=1 and d=2

Sn= n/2(2×1+(n-1)2)

Sn=n/2(2+2n-2)

Sn=n/2×2n

Sn=n2