Question

if the nth term of AP is [2n+1] find the sum of first n terms of the AP

Answer 1

Here,

nth term=2n+1

so,

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

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

a=2n+1-dn+d_____eq 1

now,

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

putting value of a in equation 2

=n/2(2(2n+1-dn+d+dn-d)

=n/2(2n+1)

therefore,

Sn=n/2(2n+1)