① (1+x)/(1-x)>0(x+1)/(x-1)<0定义域：-1② f(-x)=loga (1-x)/(1+x)=loga [(1+x)/(1-x)]^(-1)=-loga (1+x)/(1-x)=-f(x)f(x)是奇函数③ f(-1/2)=-f(1/2)=-2loga (1+1/2)/(1-1/2)=2loga (3/2)/(1/2)=2loga 3=2a^2=3∵a>0∴a=√3
