Here we have #f(x)=(sec(e^x))^(-1/2)#
#f'(x)=d/dx[(sec(e^x))^(-1/2)]#
#color(white)(f'(x))=(sec(e^x))^(-1/2-1)*-1/2*d/dx[sec(e^x)]#
#color(white)(f'(x))=(sec(e^x))^(-3/2)*-1/2*d/dx[sec(e^x)]#
#color(white)(f'(x))=(sec(e^x))^(-3/2)*-1/2*sec(e^x)tan(e^x)*d/dc[e^x]#
#color(white)(f'(x))=-(e^xsec(e^x)tan(e^x))/(2(sec(e^x))^(3/2))#
#color(white)(f'(x))=-(e^xtan(e^x))/(2(sec(e^x))^(1/2))#
#color(white)(f'(x))=-(e^xtan(e^x)sec(e^x)^(-1/2))/2#