1:
a: \(\Leftrightarrow x^2=90\)
hay \(x\in\left\{3\sqrt{10};-3\sqrt{10}\right\}\)
b: \(\Leftrightarrow x^2=36\)
=>x=6 hoặc x=-6
c: =>6x-8=4x+4
=>2x=12
hay x=6
d: =>36x=240-12x
=>48x=240
hay x=5
a) \(\dfrac{-6}{x}=\dfrac{x}{-15}\)
\(\Leftrightarrow x^2=90\)
\(\Leftrightarrow\left[{}\begin{matrix}x=3\sqrt{10}\\x=-3\sqrt{10}\end{matrix}\right.\)
b) \(\dfrac{4}{x}=\dfrac{x}{9}\)
\(\Leftrightarrow x^2=36\)
\(\Leftrightarrow\left[{}\begin{matrix}x=6\\x=-6\end{matrix}\right.\)
c) \(\dfrac{2}{x+1}=\dfrac{4}{3x-4}\)
\(\Leftrightarrow6x-8=4x+4\)
\(\Leftrightarrow2x=12\)
\(\Leftrightarrow x=6\)
d) \(\dfrac{x}{12}=\dfrac{20-x}{36}\)
\(\Leftrightarrow240-12x=36x\)
\(\Leftrightarrow48x=240\)
\(\Leftrightarrow x=5\)
