∂z/∂x=z`_(x)=(1/(x^2+y))*(x^2+y)`_(x)=2x/(x^2+y);
∂z/∂y=z`_(y)=(1/(x^2+y))*(x^2+y)`_(y)=1/(x^2+y).
6.5
gradu=(∂u/∂x)*vector{i}+(∂u/∂y)*vector{i}+(∂u/∂z)*vector{k}
∂u/∂x=(1/(3-x^2))*(3-x^2)`+y^2z*(x)`=(-2x/(3-x^2))+y^2z
∂u/∂y=0 + xz*(y^2)`=2xyz
∂u/∂z=0+xy^2*(z)`=xy^2
gradu=((-2x/(3-x^2))+y^2z)*vector{i}+(2xyz)*vector{i}+(xy^2)*vector{k}
∂u/∂x _(M)=(-2/(3-2^2))+3^2*2=2+18=20
∂u/∂y_(M)=2*1*3*2=12
∂u/∂z_(M)=1*3^2=9
gradu(M)=20*vector{i}+12*vector{i}+9*vector{k}