Did you forget to take the partial derivatives of ?
Find gradient f at the given point.
f(x,y,z)= ( (x^2+y^2+z^2)^(-1/2) ) + ln(xyz) , (-1,2,-2)
df/dx = -x/(x^2+y^2+z^2)^(3/2)
df/dy = -y/(x^2+y^2+z^2)^(3/2)
df/dz = -z/(x^2+y^2+z^2)^(3/2)
ok so after finding the partials with respect to x,y,z and plugging in the point I get the answer
-1/27 i - 2/27 j + 2/27 k
the books answer is
-26/27 i +23/54 j -23/54 k
Can anyone verify which answer is correct?