The Directional derivative of f(x,y,z) in the direction of the unit vector is the dot product, where is a unit vector in the direction of .
Let be a function with continous partial deriatives in .
Let , two directions in . Between all the directional deriatives of f in the point P, the maximal value is 11 when the deriative is in the direction of u. What is the value of ?
I know the maximal value is the value in the gradient...But have no idea how it helps us...
Hope you'll be able to help me