dz/dt = du/dt * v + dv/dt * u + dsint/dt
= u'v+v'u+cost
而u'=-sint ,v'=1/t
所以dz/dt =-sint * v + u/t + cost
=-lnt sint + cost/t +cost
dz/dt = du/dt * v + dv/dt * u + dsint/dt
= u'v+v'u+cost
而u'=-sint ,v'=1/t
所以dz/dt =-sint * v + u/t + cost
=-lnt sint + cost/t +cost