Find the directional derivative of along the curve at the point P where u = 0
My working:
At u=0, x=1, y=1, z=-1 so let u = (1,1,-1).
Know that
At u=0, x=(1,1,-1) so
However, I'm not sure if this is correct as I don't know whether I'm meant to substitute u into f to find the derivative at a specific point or not?