Question

Class 8 squares and square roots without adding find the sum of a) 1+3+5+7+9+11+13+15+17.

Answer 1

given

n=9

a=1

d=3-1=2

Explanation:

now , by formula,

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

= 9/2(2×1+(9-1)×2)

=9/2×18

=81