\(M=\frac{2x+1}{x^2+2}\Leftrightarrow Mx^2+2M=2x+1\)
\(\Leftrightarrow Mx^2+2M-2x-1=0\)
\(\Leftrightarrow Mx^2-2x+\left(2M-1\right)=0\)
\(\Delta'=1-M\left(2M-1\right)\ge0\Leftrightarrow1-2M^2+M\ge0\)
\(\Leftrightarrow\left(1-M\right)\left(1+2M\right)\ge0\)
\(\Rightarrow\frac{-1}{2}\le M\le1\)
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