u=ln(1/(x+√（y^2+z^2)))du/dx=1/ 1/(x+√（y^2+z^2)) * -1/(x+√（y^2+z^2))^2 =-(x+√（y^2+z^2))dx/(x+√（y^2+z^2))^2=-1/(x+√（y^2+z^2))du/dy=1/ 1/(x+√（y^2+z^2)) * -1/(x+√（y^2+z^2))^2 *1/2√(y^2+z^...老大。。我问题写错了。。是u=ln(x+√（y^2+z^2))。。而且是求偏导数、、不是导数u=ln(x+√（y^2+z^2))du/dx=1/(x+√（y^2+z^2))du/dy=1/(x+√（y^2+z^2)) * 1/[2√(y^2+z^2) *2y =y/[(x+√（y^2+z^2))√(y^2+z^2)] du/dz=z/[(x+√（y^2+z^2))√(y^2+z^2)]