\(\left(1+\dfrac{1}{2x}\right).lg3+lg2=lg\left(27-3^{\dfrac{1}{x}}\right)\)
\(\Leftrightarrow lg3^{1+\dfrac{1}{2x}}+lg2=lg\left(27-3^{\dfrac{1}{x}}\right)\)
\(\Leftrightarrow lg\left(2.3^{1+\dfrac{1}{2x}}\right)=lg\left(27-3^{\dfrac{1}{x}}\right)\)
\(\Leftrightarrow2.3^{1+\dfrac{1}{2x}}=27-3^{\dfrac{1}{x}}\)
\(\Leftrightarrow2.3.\left(3^{\dfrac{1}{x}}\right)^2=27-3^{\dfrac{1}{x}}\)
Đặt \(3^{\dfrac{1}{x}}=t\left(t>0\right)\) phương trình trở thành:
\(2.3t^2=27-t\)
\(\Leftrightarrow\left[{}\begin{matrix}t_1=\dfrac{-1-\sqrt{649}}{12}\left(l\right)\\t_2=\dfrac{1+\sqrt{649}}{12}\left(tm\right)\end{matrix}\right.\)
Với \(t=\dfrac{-1-\sqrt{649}}{12}\Leftrightarrow3^{\dfrac{1}{x}}=\dfrac{-1-\sqrt{649}}{12}\)
\(\Leftrightarrow\dfrac{1}{x}=log^{\dfrac{-1-\sqrt{649}}{12}}_3\)
\(\Leftrightarrow x=log^3_{\dfrac{-1-\sqrt{649}}{12}}\).
