For a CDF F(x)=1−e−xF(x) = 1 - e^{-x}F(x)=1−e−x for x>=0x >= 0x>=0, what is the PDF?
f(x) = e^{-x}
f(x) = 1 - e^{-x}
f(x) = x*e^{-x}
f(x) = -e^{-x}