#f(x)=ln(sqrt(e^x-x))#
#f'(x) = 1/(sqrt(e^x-x)) * d/dx(sqrt(e^x-x))# (Standard differential and chain rule)
#= 1/(sqrt(e^x-x)) * 1/2(e^x-x)^(-1/2) * d/dx(e^x-x)# (Power rule and chain rule)
#=1/(sqrt(e^x-x)) * 1/(2 (sqrt(e^x-x))) *(e^x-1)# (Standard differential and power rule)
#= (e^x-1)/(2(e^x-x))#