tìm x biết
\(\dfrac{1}{27x^2\left(x+1\right)-\left(3x+1\right)^3}=-8\)
Tìm dc x = \(\dfrac{-7}{72}\)
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\(\dfrac{1}{27x^2\left(x+1\right)-\left(3x+1\right)^3}=-8\)
\(\Leftrightarrow\) \(-8.\left(27x^2\left(x+1\right)-\left(3x+1\right)^3\right)\) = 1
\(\Leftrightarrow\) \(-8.\left(27x^3+27x^2-27x^3-27x^2-9x-1\right)\) =1
\(\Leftrightarrow\) \(72x+8=1\)
\(\Leftrightarrow72x=\)-7
\(\Leftrightarrow x=-\dfrac{72}{7}\)
Vậy x = \(-\dfrac{72}{7}\)
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