f(x)=log(x+√x^2+1)的定义域Rf(-x)=log(-x+√x^2+1)=log(-x+√x^2+1)((x+√x^2+1)/(x+√x^2+1)=log[1/(x+√x^2+1)]=-log(x+√x^2+1)=-f(x)f(x)是奇函数定义域是R是怎么证明的？x^2+1>x^2√x^2+1>|x|>=x