Đáp án:
$\begin{array}{l}
Đkxđ:4 - x \ge 0 \Rightarrow x \le 4\\
\left\{ \begin{array}{l}
\left( {5 - x} \right)\sqrt {4 - x} = 0\left( 1 \right)\\
\sqrt[3]{{x + 5}} + 3\sqrt y = 4\left( 2 \right)
\end{array} \right.\\
\left( 1 \right) \Rightarrow \left[ \begin{array}{l}
x = 5\left( {ktm} \right)\\
x = 4\left( {tm} \right)
\end{array} \right.\\
Thay\,x = 4\,vao\left( 2 \right):\sqrt[3]{{4 + 5}} + 3\sqrt y = 4\\
\Rightarrow 3\sqrt y = 4 - \sqrt[3]{9}\\
\Rightarrow y = \frac{{16 - 8\sqrt[3]{9} + \sqrt[3]{{81}}}}{9}\\
\Rightarrow \left( {x;y} \right) = \left( {4;\frac{{16 - 8\sqrt[3]{9} + \sqrt[3]{{81}}}}{9}} \right)
\end{array}$
