Question

If nth term of an ap is 2n+1 find the sum of first n terms of ap

Answer 1

Step-by-step explanation:

aN=2n+1

taking n=1,2

a1=2×1+1

=2+1=3

a2=2×2+1

=4+1=5

d=a2-a1

=5-3=2

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

=n/2[2×3+(n-1)2]

=n/2[6+2n-2]

=n/2[4+2n]

=2n+n sq.