Toán Cho E = 4x / căn x-3 . Tìm x để căn A+3 ( 3 nằm trong căn A ) – căn A =1 04/10/2021 By Savannah Cho E = 4x / căn x-3 . Tìm x để căn A+3 ( 3 nằm trong căn A ) – căn A =1
\[\begin{array}{l} A = \frac{{4x}}{{\sqrt x – 3}}\,\,\,\,\\ DK:\,\,\,x \ge 0;\,\,\,x \ne 9.\\ \sqrt {A + 3} – \sqrt A = 1\,\,\,\,\,\,\,\,\left( {A \ge 0} \right)\\ \Leftrightarrow \sqrt {A + 3} = 1 + \sqrt A \\ \Leftrightarrow A + 3 = 1 + A + 2\sqrt A \\ \Leftrightarrow 2\sqrt A = 2\\ \Leftrightarrow \sqrt A = 1\\ \Leftrightarrow A = 1\\ \Leftrightarrow \frac{{4x}}{{\sqrt x – 3}}\, = 1\\ \Leftrightarrow 4x = \sqrt x – 3\\ \Leftrightarrow 4x – \sqrt x + 3 = 0\\ \Leftrightarrow pt\,\,\,VN.\\ Vay\,\,k\,\,\,co\,\,\,x\,\,\,thoa\,\,man. \end{array}\] Trả lời
\[\begin{array}{l}
A = \frac{{4x}}{{\sqrt x – 3}}\,\,\,\,\\
DK:\,\,\,x \ge 0;\,\,\,x \ne 9.\\
\sqrt {A + 3} – \sqrt A = 1\,\,\,\,\,\,\,\,\left( {A \ge 0} \right)\\
\Leftrightarrow \sqrt {A + 3} = 1 + \sqrt A \\
\Leftrightarrow A + 3 = 1 + A + 2\sqrt A \\
\Leftrightarrow 2\sqrt A = 2\\
\Leftrightarrow \sqrt A = 1\\
\Leftrightarrow A = 1\\
\Leftrightarrow \frac{{4x}}{{\sqrt x – 3}}\, = 1\\
\Leftrightarrow 4x = \sqrt x – 3\\
\Leftrightarrow 4x – \sqrt x + 3 = 0\\
\Leftrightarrow pt\,\,\,VN.\\
Vay\,\,k\,\,\,co\,\,\,x\,\,\,thoa\,\,man.
\end{array}\]