a: Ta có: \(M=\left(\dfrac{1}{2x-y}-\dfrac{-x^2+3y-2}{4x^2-y^2}-\dfrac{2}{2x+y}\right):\left(\dfrac{x^2+y^2}{4x^2-y^2}+1\right)\)
\(=\dfrac{2x+y+x^2-3y+2-4x+2y}{\left(2x-y\right)\left(2x+y\right)}:\dfrac{x^2+y^2+4x^2-y^2}{\left(2x-y\right)\left(2x+y\right)}\)
\(=\dfrac{x^2-2x+2}{5x^2}\)
c: Ta có: \(\left\{{}\begin{matrix}x^2-2x+2=\left(x-1\right)^2+1>0\forall x\\5x^2>0\forall xtmĐKXĐ\end{matrix}\right.\)
Do đó: M>0