tìm x biết 2 √9x trừ 27 trừ 1/5 √25x trừ 75 trừ 1/7 √49x trừ 147 = 20 22/07/2021 Bởi Katherine tìm x biết 2 √9x trừ 27 trừ 1/5 √25x trừ 75 trừ 1/7 √49x trừ 147 = 20
Đáp án: $\begin{array}{l}Dkxd:x \ge 3\\2\sqrt {9x – 27} – \dfrac{1}{5}.\sqrt {25x – 75} – \dfrac{1}{7}\sqrt {49 – 147} = 20\\ \Rightarrow 2.3\sqrt {x – 3} – \dfrac{1}{5}.5\sqrt {x – 3} – \dfrac{1}{7}.7\sqrt {x – 3} = 20\\ \Rightarrow 6\sqrt {x – 3} – \sqrt {x – 3} – \sqrt {x – 3} = 20\\ \Rightarrow 4\sqrt {x – 3} = 20\\ \Rightarrow \sqrt {x – 3} = 5\\ \Rightarrow x – 3 = 25\\ \Rightarrow x = 28\left( {tmdk} \right)\\Vay\,x = 28\end{array}$ Bình luận
Đáp án:
$\begin{array}{l}
Dkxd:x \ge 3\\
2\sqrt {9x – 27} – \dfrac{1}{5}.\sqrt {25x – 75} – \dfrac{1}{7}\sqrt {49 – 147} = 20\\
\Rightarrow 2.3\sqrt {x – 3} – \dfrac{1}{5}.5\sqrt {x – 3} – \dfrac{1}{7}.7\sqrt {x – 3} = 20\\
\Rightarrow 6\sqrt {x – 3} – \sqrt {x – 3} – \sqrt {x – 3} = 20\\
\Rightarrow 4\sqrt {x – 3} = 20\\
\Rightarrow \sqrt {x – 3} = 5\\
\Rightarrow x – 3 = 25\\
\Rightarrow x = 28\left( {tmdk} \right)\\
Vay\,x = 28
\end{array}$