Find the directions in which the function increases and decreases most rapidly at Po. Then find the derivatives of the function in these directions.
f(x,y) = x² + xy + y², Po(-4,4)
The derivative of the given function f(x,y) = x² + xy + y² in the direction in which the function increases most rapidly at Po(-4,4) is (Duf) (-4,4) =
(Type an exact answer, using radicals as needed.)