Bài 1:
\(\dfrac{x}{x^2+x+1}=\dfrac{-2}{3}\)
\(\Leftrightarrow-2x^2-2x-2=3x\)
\(\Leftrightarrow-2x^2-2x-2-3x=0\)
\(\Leftrightarrow-2x^2-5x-2=0\)
\(\Leftrightarrow-\left(2x^2+4x+x+2\right)=0\)
\(\Leftrightarrow-\left(x+2\right)\left(2x+1\right)=0\)
\(\Leftrightarrow\left[{}\begin{matrix}x+2=0\\2x+1=0\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}x=-2\\x=-\dfrac{1}{2}\end{matrix}\right.\)
Với x = - 2:
\(M=\dfrac{\left(-2\right)^2}{\left(-2\right)^4+\left(-2\right)^2+1}=\dfrac{4}{16+4+1}=\dfrac{4}{21}\)
Với \(x=-\dfrac{1}{2}\) :
\(\dfrac{\left(-\dfrac{1}{2}\right)^2}{\left(-\dfrac{1}{2}\right)^4+\left(-\dfrac{1}{2}\right)^2+1}=\dfrac{\dfrac{1}{4}}{\dfrac{1}{16}+\dfrac{1}{4}+1}=\dfrac{\dfrac{1}{4}}{\dfrac{21}{16}}=\dfrac{4}{21}\)
