Question

Tịm x

\(27\left(3x-1\right)^3=-|-8|\)

\(\dfrac{2x}{-15}=\dfrac{-120}{x}\)

Answer 1

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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