The gradient of f(x,y,z)=1x2+y2+z2f(x,y,z) = \frac{1}{\sqrt{x^2 + y^2 + z^2}}f(x,y,z)=x2+y2+z21 at the point (1,2,2)(1,2,2)(1,2,2) is proportional to which vector?
(1,2,2)(1, 2, 2)(1,2,2)
(−1,−2,−2)(-1, -2, -2)(−1,−2,−2)
(1,2,2)/3(1, 2, 2)/3(1,2,2)/3
(−1,−2,−2)/27(-1, -2, -2)/27(−1,−2,−2)/27