My function is: Z = f(x,y) = (x^2/25)+(y^2/100)
and I have to find the directional derivatives
(grad Z.u, grad Z.v) from point A(3,3,0.45) to
points B(6,-3,1.53) and C(-6,3,1.53).
AB = 3i-6j, Unit vector in the direction of AB,
u = i/(5^.5)-2j/(5^.5)
AC = -9i , Unit vector in the direction of AC,
v = -i
Grad Z = (2x/25)i+(2y/100)j
and then
Grad Z at(3,3)=(6/25)i+(3/50)j
grad Z.u = [6/25)i+(3/50)j].[i/(5^.5)-2j/(5^.5)]
= 0.05366563146
grad Z.v=[6/25)i+(3/50)j].[-i]
= -0.24
