对log(tanx+secx)求导

(ln(tanx+secx))'
=(tanx+secx）'/(tanx+secx)
=(1/(cosx)^2+sinx/(cosx)^2)/(tanx+secx)
=(1/(cosx)^2+sinx/(cosx)^2)/(sinx/cosx+1/cosx)
=1/cosx