#f'=((arc tan (e^x-1))^(-1/2))'#
#=-1/2(arc tan (e^x-1))^(-3/2)(aec tan(e^x-1))'#
#=-1/2(arc tan (e^x-1))^(-3/2)(1/(1+(e^x-1)^2))((e^x-1)'#
#=-1/2(arc tan (e^x-1))^(-3/2)(1/(1+(e^x-1)^2))(e^x)#
#=-e^x/(2((2-2e^x+e^(2x)) arc tan (e^x-1)sqrt(arc tan (e^x-1)))#