Question

Answer 1

ĐKXĐ: \(x\ne\left\{0;\pm3\right\}\)

\(A=\left(\dfrac{-\left(x-3\right)\left(x+3\right)^2}{\left(x+3\right)\left(x+3\right)\left(x-3\right)}+\dfrac{x}{x+3}\right):\dfrac{3x^2}{x+3}\)

\(=\left(-1+\dfrac{x}{x+3}\right):\dfrac{3x^2}{x+3}=\dfrac{-3}{x+3}.\dfrac{x+3}{3x^2}\)

\(=-\dfrac{1}{x^2}\)

Với \(x=-\dfrac{1}{2}\Rightarrow A=-\dfrac{1}{\left(-\dfrac{1}{2}\right)^2}=-4\)

Do \(-\dfrac{1}{x^2}< 0;\forall x\Rightarrow A< 0\) với mọi x thuộc TXĐ \(\Rightarrow x\ne\left\{0;\pm3\right\}\)