（I）f（x）=x-x-1的定义域为{x|x≠0}，f（-x）=-x+x-1=-f（x）∴函数f（x）为奇函数（II）任取x1，x2∈（0，+∞），不妨设x1＜x2，则有f(x1)−f(x2)＝x1−1x1−(x2−1x2)＝(x1−x2)+(1x2−1x1)＝(x1−x2)+(x1−x2x1...