F'xy^x/z*lny^1/z=z*cosx
F'y=x/z*y^(x/z-1)=0
F'z=-x/z/y^(x/z-1)*x/sqrt(z)=sinx=-x^2/sqrt(z^3)*y^(x/z-1)=sinx
dz/dx=0, dz/dy=Pi/4
dz(A)=Pi/4
Верно?