Question

Find the directional derivative of f(x,y,z)=yx+z^3 at the point (3,2,1) in the direction of a vector making an angle of pi/4 with the gradient of f(x,y,z) at (3,2,1)

Answer 1

The gradient of f(x,y,z) is <f_x,f_y,f_z>=<y,x,3z^2>. Correct? Thus, at (3,2,1), the gradient is <2,3,3>.

Answer 2

How do I find a vector with a 45 degree angle between it and a given vector?

Answer 3

okay