For $f(x,y),$ find all values of $x$ and $y$ such that $f_x(x,y)=0$ and $f_y(x,y)=0$ simultaneously.

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$14.[-/4$ Points$]$

LARCCALC$1213\mathrm{.}3\mathrm{.}079.0/100$ Submissions Used

Find the four second partial derivatives. Observe that the second mixed partials are equal.

$,z=x^4-3xy+9y^3$

$\frac{de{l}^{2}z}{del{x}^2}=$

$\frac{de{l}^{2}z}{\text{d}\text{e}\text{l}\text{y}\text{d}\text{e}\text{l}\text{x}}=$

$\frac{de{l}^{2}z}{del{y}^2}=$

$\frac{de{l}^{2}z}{\text{d}\text{e}\text{l}\text{x}\text{d}\text{e}\text{l}\text{y}}=$

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$15.[-/4$ Points$]$

LARCALC$1213\mathrm{.}3\mathrm{.}084.\frac{0}{100}$ Submissions Used

Find the four second partial derivatives, Observe that the second mixed partials are equal.

$\frac{de{l}^{2}z}{del{x}^2}=$

$\frac{de{l}^{2}z}{\text{d}\text{e}\text{l}\text{y}\text{d}\text{e}\text{l}\text{x}}=$

$\frac{de{l}^{2}z}{del{y}^2}=$

$\frac{de{l}^{2}z}{\text{d}\text{e}\text{l}\text{x}\text{d}\text{e}\text{l}\text{y}}=$