Question

z=x^y,x=sint,y=tant,求全导数。

Answer 1

lnz=y*lnx=tant*lnsint
两边同时求导：
dz/z=sec^2t*lnsintdt+tant*cost/sintdt
dz=z(sec^2t*lnsint+tan^2t)dt.
dz=(sint)^(tant)*(sec^2t*lnsint+tan^2t)dt.

Answer 2

解:
dz/dt=偏z/偏x×偏x/偏t+偏z/偏y×偏y/偏t
=(yx^(y-1))(cost)+(x^y(lnx))((sect)^2)
=tantcost[(sint)^(tnat-1)] + [(sect)^2][lnsint][(sint)^(tant)]