f(x)+f(1/x)=(x-1)/(x+1)+(1/x-1)/(1/x+1)=(x-1)/(x+1)+((1-x)/x)/((1+x)/x)=(x-1)/(x+1)+(1-x)/(1+x)=(x-1+1-x)/(1+x)=0f(1/x)就是所在函数等式中 的x=1/x,具体例子看上面
f(1/x)=(x-1)/(x+1)f(x)=(1/x -1)/(1/x +1)=(1-x)/(1+x)f(x)+f(1/x)=0