\(\left(x-2\right)\left(x+4\right)< \dfrac{5}{x^2+2x+2}-6\)
\(\Leftrightarrow x^2+2x-8< \dfrac{5}{x^2+2x+2}-6\)
\(\Leftrightarrow\left(x^2+2x-8\right)\left(x^2+2x+2\right)< 5-6\left(x^2+2x+2\right)\) (vì \(x^2+2x+2>0\forall x\))
\(\Leftrightarrow\left(x^2+2x+2\right)^2-10\left(x^2+2x+2\right)< 5-6\left(x^2+2x+2\right)\)
\(\Leftrightarrow\left(x^2+2x+2\right)^2-4\left(x^2+2x+2\right)-5< 0\)
\(\Leftrightarrow\left(x^2+2x-3\right)\left(x^2+2x+3\right)< 0\)
\(\Leftrightarrow x^2+2x-3< 0\)
\(\Leftrightarrow-3< x< 1\)
=> S=(-3;1)
=>P=-4 ý D
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