2y Suppose f(x, y) = sin X in the direction of (1, 2). Then, 2y 2y i (a) ▼ f(x, y) = cos(2)21 +21) X (b) ▼ ƒ(6, π) = COS and u is the unit vector 1/2 ( - 1 3 ² + 1) i 18 3 (c) fu (6, π) = Du ƒ(6, π) = in 36 + 6

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Find the directional derivative Duf(1, 1), where f(x, y) = x2 + y2 and u is the unit vector at an angle of π/6 from horizontal.

Determine the directional derivative of the function f(x, y) = -5y³ r - 1 at the point (x, y) = (2, -3) in the direction of the vector u shown in the figure below: 135⁰ U You can use the fact that Vf(x, y) = (-5y³, -15 y² z). State your answer exactly Du f(2, -3) =