设f(x)=1+x^2/1-x^2,求证:
(1)f(-x)=f(x)
(2)f(1/x)=-f(x)
(1)f(-x)=1+(-x)^2/1-(-x)^2=1+x^2/1-x^2=f(x)
(2)f(1/x)=1+(1/x)^2/1-(1/x)^2=(1+1/x^2)/(1-1/x^2)=(x^2+1)/(x^2-1)=-f(x)