High School

What is the directional derivative of [tex]f(x, y, z) = z^3 - x^2y[/tex] at the point (2, -5, -5) in the direction of the vector [tex]\mathbf{v} = \langle -4, 1, 4 \rangle[/tex]?

A. 39
B. -39
C. 49
D. -49

Answer :

Final answer:

The directional derivative of the function f(x, y, z) = z^3 - x^2 * y at the point (2, -5, -5) in the direction of the vector v = (-4, 1, 4) is -300.

Explanation:

The directional derivative of the function f(x, y, z) = z^3 - x^2 * y at the point (2, -5, -5) in the direction of the vector v = (-4, 1, 4) can be found using the formula:

D_v f(x, y, z) = gradient(f) * v

Plugging in the values, we can calculate:

D_v f(2, -5, -5) = (3z^2, -2xy, x^2) * (-4, 1, 4)

Simplifying, we get:

D_v f(2, -5, -5) = (-300, 20, -400)

So the directional derivative of the function in the given direction is -300.