a. \(27\left(3x-1\right)^3=-\left|-8\right|\)
\(\Rightarrow27\left(3x-1\right)^3=-8\)
\(\Rightarrow\left(3x-1\right)^3=-8:27\)
\(\Rightarrow\left(3x-1\right)^3=\dfrac{-8}{27}\)
\(\Rightarrow\left(3x-1\right)^3=\left(-\dfrac{2}{3}\right)^3\)
\(\Rightarrow3x-1=\dfrac{-2}{3}\)
\(\Rightarrow3x=\dfrac{-2}{3}+1=\dfrac{1}{3}\)
\(\Rightarrow x=\dfrac{1}{3}:3=\dfrac{1}{9}\)
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b. \(\dfrac{2x}{-15}=\dfrac{-120}{x}\)
\(\Leftrightarrow2x.x=\left(-15\right).\left(-120\right)\)
\(\Rightarrow2.x^2=1800\)
\(\Rightarrow x^2=1800:2=900\)
\(\Rightarrow x^2=\left(\pm30\right)^2\)
\(\Rightarrow\left[{}\begin{matrix}x=30\\x=-30\end{matrix}\right.\)
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