Question

1 If ϕ=2xz4−x2y, find |▽ϕ|
2 If ϕ(x,y,z)=3x^2y−y^3z^2, find ▽ϕ at point (1,-2,-1)
3 Find a unit normal to the surface x^2y+2xz=4 at point (2,-2,3)
4 Let ϕ(x,y,z)=xy^2z and A=xzi−xy^2j+yz2k,find ∂^3/∂x^2∂z (ϕA)