QUICK CHECK EXERCISES 15.1
(See page 1093 for an
1. The function \( \phi(x, y, z)=x y+y z+x z \) is a potential for the vector field \( \mathbf{F}= \)
2. The vector field \( \mathbf{F}(x, y, z)= \) \( \qquad \) defined for \( (x, y, z) \neq(0,0,0) \), is always directed toward the origin and is of length equal to the distance from \( (x, y, z) \) to the origin.