Question

   bài 6b,7a,7b  

Answer 1

6B.
a)\(\sqrt[3]{4-2x}\ge4\Leftrightarrow4-2x\ge64\)
\(\Leftrightarrow2x\le-60\Leftrightarrow x\le-30\)
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b) \(\sqrt[3]{-x^3-3x^2+6x-10}< -x-1\)

\(\Leftrightarrow-x^3-3x^2+6x-10< -\left(x+1\right)^3\)

\(\Leftrightarrow-x^3-3x^2+6x-10< -x^3-3x^2-3x-1\)

\(\Leftrightarrow9x< 9\Leftrightarrow x< 1\)
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7A.
a) \(\sqrt[3]{2x+1}=3\Leftrightarrow2x+1=27\Leftrightarrow x=13\)
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b) \(\sqrt[3]{5+x}-x=5\)

\(\Leftrightarrow5+x=\left(5+x\right)^3\) \(\Leftrightarrow\left[{}\begin{matrix}5+x=0\\\left(5+x\right)^2=1\end{matrix}\right.\)\(\Leftrightarrow\left[{}\begin{matrix}x=-5\\x=-4\\x=-6\end{matrix}\right.\)

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7B.

a) PT \(\Leftrightarrow2-3x=-8\Leftrightarrow x=\dfrac{10}{3}\)

b) PT \(\Leftrightarrow x-1=\left(x-1\right)^3\) 

\(\Leftrightarrow\left(x-1\right)\left[1-\left(x-1\right)^2\right]=0\)

\(\Leftrightarrow\left[{}\begin{matrix}x-1=0\\\left(x-1\right)^2=1\end{matrix}\right.\) \(\Leftrightarrow\left[{}\begin{matrix}x=1\\x=0\\x=2\end{matrix}\right.\)

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