\(K=\dfrac{4x^2+4-4x^2-4x-1}{2x^2+2}=2-\dfrac{\left(2x+1\right)^2}{2x^2+2}\le2\)
\(K_{max}=2\) khi \(x=-\dfrac{1}{2}\)
\(K=\dfrac{-x^2-1+x^2-4x+4}{2x^2+2}=-\dfrac{1}{2}+\dfrac{\left(x-2\right)^2}{2x^2+2}\ge-\dfrac{1}{2}\)
\(K_{min}=-\dfrac{1}{2}\) khi \(x=2\)