I am suppose to find the directional derivative for the function f(x,y,z) = xy + z^2
at the point (2,3,4) in the direction of a vector making an angle of 3pi/4 with the grad f(2,3,4)
I have done several with this function with other specific directions but this one is confusing me.
I know the grad is y i + x J + 2z k so at (2,3,4) this would be 3i + 2j + 8 k but where do I go from here???? Please someone nudge or push me in the correct direction!!!! Thanks
I remember that the dot product of two vectors is equal to their magnitude's multiplied by the cos of the angle between them but since I do not have v or mag of v how does this allow me to solve this question???? I am still lost.