ok so heres the question: find the directional derivative of the function f(x,y,z)=xy+yz+zx at the P(3,-3,4) in the direction of Q(7,1,7)...

Here's what I have done:

found partial derivatives and added them to give the gradient

(y+z)i+(x+z)j+(y+x)k

plugging in P gives: (-3+4)i+(3+4)j+(-3+3)K = i+7j

since v is not a unit vector, i took the magnitude of Q and got sqrt(99)

I got: 7/sqrt(99)i+1/sqrt(99)j+7/sqrt(99)

so the gradient times the Q gives 14/sqrt(99)

but for some reason webassign says this answer is incorrect, can someone please help, I appreciate it