Answer
$3+6\sqrt3$
Work Step by Step
Formula to calculate the directional derivative: $D_uf=f_x(x,y)a+f_y(x,y)b$
$D_uf=(y^3-2x) \times \cos (\pi/3)+(3xy^2) \times \sin (\pi/3)$
This implies
At $(1,2)$
$D_uf=6 \times \dfrac{1}{2}+12 \times \dfrac{\sqrt 3}{2}$
$D_uf =3+6\sqrt3$
