Find the Hessian matrix HfH_fHf of f(x,y)=x3+y3f(x, y) = x^3 + y^3f(x,y)=x3+y3.
(6x006y)\begin{pmatrix} 6x & 0 \\ 0 & 6y \end{pmatrix}(6x006y)
(3x2003y2)\begin{pmatrix} 3x^2 & 0 \\ 0 & 3y^2 \end{pmatrix}(3x2003y2)
(6006)\begin{pmatrix} 6 & 0 \\ 0 & 6 \end{pmatrix}(6006)
(0660)\begin{pmatrix} 0 & 6 \\ 6 & 0 \end{pmatrix}(0660)