\textbf{4.} Spo�t�te parci�ln� derivace 1. a 2. ��du funkce
    $u = \frac x{y^2}$

    \textbf{�e�en�}
    \begin{align*}
        \frac{\partial u}{\partial x} &= \frac 1{y^3}\\
        \frac{\partial u}{\partial y} &= \frac{-2x}{y^3}\\
        \frac{\partial^2 u}{\partial x \partial y} &= -\frac2{y^3}\\
        \frac{\partial^2 u}{\partial y \partial x} &= -\frac2{y^3}\\
        \frac{\partial^2 u}{\partial x^2} &= 0\\
        \frac{\partial^2 u}{\partial y^2} &= \frac{6x}{y^4}
    \end{align*}
