A>0 So an x > 0 denominator 1+ an x > 0 domain is an r domain that is symmetric about the origin.

f(-x)=( 1-a^(-x))/( 1+a^(-x))=( 1- 1/a^x)( 1+ 1/a^x)=(a^x- 1)/(a^x+ 1)=-f(x)

So f(x) is odd function.