Question

find the sum if 1+3+5+7+9+.....25​

Answer 1

a=1

d=3-1

d=2

an=25

a+(n-1)d=25

1+(n-1)2=25

(n-1)2 =24

n-1=12

n=13

Sn=n/2(a+an)

Sn=13/2(1+25)

=13/2×26

=13×13

Sn=169