Finding the Directional derivative

[teng125]

Find the directional derivative of f (x, y) = 5−x2−2y2 at P (-1, -1).
anybody pls help as i don't know how to find the direction from this ques so , i can't find the directional derivative


pls help
thanx

 

[neutrino]

Your question seems to be incomplete; please provide the complete question as it is given in the book. The directional derivative is the rate at which a function changes at some point in a particular direction.

 

[Office_Shredder]

The directional derivative is the rate at which a function changes at some point in a particular direction.

anybody pls help as i don't know how to find the direction from this ques so

I think that's what he's trying to figure out.

If you have absolutely no clue what direction it's in, I would guess that it's in the direction of the vector from the origin to P. Not for any particular reason, but because it's a better guess than anything else

 

[Astronuc]

http://mathworld.wolfram.com/DirectionalDerivative.html

Does the problem call for the directional derivative of the tangent, normal, or perhaps the directional derivative greatest magnitude?

 

[HallsofIvy]

One more time: the problem as stated makes no sense. teng125, please state the entire problem as given in your textbook.