b) \(2x^3-50x=0\)
\(\Leftrightarrow2\left(x^2-25\right)=0\)
\(\Leftrightarrow x^2-25=0\)
\(\Leftrightarrow\left(x-5\right)\left(x+5\right)=0\)
\(\Leftrightarrow\left[{}\begin{matrix}x-5=0\\x+5=0\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}x=5\\x=-5\end{matrix}\right.\)
Vậy \(x\in\left\{5;-5\right\}\)
a) \(\left(x+2\right)\left(x^2-2x+4\right)-x\left(x-1\right)\left(x+1\right)+3x=2\)
\(\Leftrightarrow x^3+2^3-x\left(x^2-1\right)+3x=2\)
\(\Leftrightarrow x^3+8-x^3+x+3x=2\)
\(\Leftrightarrow4x+8=2\)
\(\Leftrightarrow4x=-6\)
\(\Leftrightarrow x=-\frac{3}{2}\)
Vậy \(x=-\frac{3}{2}\)
c) \(5x^2-4\left(x^2-2x+1\right)-5=0\)
\(\Leftrightarrow5x^2-4x^2+8x-4-5=0\)
\(\Leftrightarrow x^2+8x-9=0\)
\(\Leftrightarrow x^2+9x-\left(x+9\right)=0\)
\(\Leftrightarrow x\left(x+9\right)-\left(x+9\right)=0\)
\(\Leftrightarrow\left(x-1\right)\left(x+9\right)=0\)
\(\Leftrightarrow\left[{}\begin{matrix}x-1=0\\x+9=0\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}x=1\\x=-9\end{matrix}\right.\)
Vậy \(x\in\left\{1;-9\right\}\)
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