50.已知函数f(x)=ex−ax−1f(x)=e^{x}-ax-1f(x)=ex−ax−1. (1)讨论函数f(x)f(x)f(x)的单调性; (2)若f(x)f(x)f(x)有且仅有2个零点,求实数aaa的取值范围.