a: \(=\dfrac{\left(x+2\right)^2}{x}\cdot\dfrac{x+2-x^2}{x+2}-\dfrac{x^2+6x+4}{x}\)
\(=\dfrac{\left(-x^2+x+2\right)\left(x+2\right)}{x}-\dfrac{x^2+6x+4}{x}\)
\(=\dfrac{-x^3-2x^2+x^2+2x+2x+4-x^2-6x-4}{x}\)
\(=\dfrac{-x^3-2x^2-2x}{x}=-x^2-2x-2\)
b,c: A=-(x^2+2x+2)
=-(x^2+2x+1+1)
=-(x+1)^2-1<=-1<0 với mọi x
Dấu = xảy ra khi x=-1