Question

express 81 as the sum of 9 odd number

Answer 1

9*9=81

9+9+9+9+9+9+9+9+9=81

Answer 2

1+3+5+7+9+11+13+15+17=81

because every square Number can be expressed in odd number

In this 81 is square of 9 so 81 is sum of first 9 odd number

It property also that :

n^2=sum of first n odd number

(here n is variable)