\(\Leftrightarrow7\cdot\left(x+\dfrac{1}{x}\right)-2\left[\left(x+\dfrac{1}{x}\right)^2-2\right]=9\)
\(\Leftrightarrow-2\left(x+\dfrac{1}{x}\right)^2+4+7\left(x+\dfrac{1}{x}\right)=9\)
\(\Leftrightarrow2\left(x+\dfrac{1}{x}\right)^2-7\left(x+\dfrac{1}{x}\right)+5=0\)
\(\Leftrightarrow\left(x+\dfrac{1}{x}-1\right)\left(2x+\dfrac{2}{x}-5\right)=0\)
\(\Leftrightarrow\dfrac{x^2-x+1}{x}\cdot\dfrac{2x^2+2-5x}{x}=0\)
\(\Leftrightarrow2x^2-5x+2=0\)
=>(x-2)(2x-1)=0
=>x=1/2 hoặc x=2
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