Giải hệ phương trình : $\left\{\begin{array}{l}(5-x)\sqrt{4-x}=0\\\sqrt[3]{x+5}+3\sqrt{y}=4\end{array}\right.$ 20/07/2021 Bởi Lydia Giải hệ phương trình : $\left\{\begin{array}{l}(5-x)\sqrt{4-x}=0\\\sqrt[3]{x+5}+3\sqrt{y}=4\end{array}\right.$
Đáp án: $\begin{array}{l}Đkxđ:4 – x \ge 0 \Rightarrow x \le 4\\\left\{ \begin{array}{l}\left( {5 – x} \right)\sqrt {4 – x} = 0\left( 1 \right)\\\sqrt[3]{{x + 5}} + 3\sqrt y = 4\left( 2 \right)\end{array} \right.\\\left( 1 \right) \Rightarrow \left[ \begin{array}{l}x = 5\left( {ktm} \right)\\x = 4\left( {tm} \right)\end{array} \right.\\Thay\,x = 4\,vao\left( 2 \right):\sqrt[3]{{4 + 5}} + 3\sqrt y = 4\\ \Rightarrow 3\sqrt y = 4 – \sqrt[3]{9}\\ \Rightarrow y = \frac{{16 – 8\sqrt[3]{9} + \sqrt[3]{{81}}}}{9}\\ \Rightarrow \left( {x;y} \right) = \left( {4;\frac{{16 – 8\sqrt[3]{9} + \sqrt[3]{{81}}}}{9}} \right)\end{array}$ Bình luận
Đáp án:
$\begin{array}{l}
Đkxđ:4 – x \ge 0 \Rightarrow x \le 4\\
\left\{ \begin{array}{l}
\left( {5 – x} \right)\sqrt {4 – x} = 0\left( 1 \right)\\
\sqrt[3]{{x + 5}} + 3\sqrt y = 4\left( 2 \right)
\end{array} \right.\\
\left( 1 \right) \Rightarrow \left[ \begin{array}{l}
x = 5\left( {ktm} \right)\\
x = 4\left( {tm} \right)
\end{array} \right.\\
Thay\,x = 4\,vao\left( 2 \right):\sqrt[3]{{4 + 5}} + 3\sqrt y = 4\\
\Rightarrow 3\sqrt y = 4 – \sqrt[3]{9}\\
\Rightarrow y = \frac{{16 – 8\sqrt[3]{9} + \sqrt[3]{{81}}}}{9}\\
\Rightarrow \left( {x;y} \right) = \left( {4;\frac{{16 – 8\sqrt[3]{9} + \sqrt[3]{{81}}}}{9}} \right)
\end{array}$