Find the directional derivative of the function at a given point P in the direction of the vector V:
f(x,y,z)= square root of xyz P(2,4,2) V=(4,2,-4)
and
f(x,y,z)= z^3 - (x^2)(y) P(1,6,2) V=(3,4,12)
Directional derivatives and gradients are investigated.