(27*u^(1/3))=27*(1/3)*u^(-2/3)*u`=9u`/∛(u)^2
и так три раза
f`_(x)=9(x+y^2+z^3)`_(x)/∛(x+y^2+z^3)^2=9/∛(x+y^2+z^3)^2
f`_(y)=9(x+y^2+z^3)`_(y)/∛(x+y^2+z^3)^2=9*2y/∛(x+y^2+z^3)^2=
=18y/∛(x+y^2+z^3)^2
f`_(z)=9(x+y^2+z^3)`_(z)/∛(x+y^2+z^3)^2=9*3z^2/∛(x+y^2+z^3)^2=
=27z^2/∛(x+y^2+z^3)^2
Теперь в точке М_(о)(3;4;2)
f`_(x)(M_(o))=9/∛(3+4^2+2^3)^2=9/∛27=3
f`_(y)(M_(o))=18*4/∛27=24
f`_(z)(M_(o))=27*2^2/∛27=4