\(A=\dfrac{6x}{x^2-9}-\dfrac{5x}{3-x}+\dfrac{x}{x+3}\)
\(ĐKXĐ:x\ne\pm3\)
\(\Leftrightarrow\dfrac{6x+5x^2+15x+x^2-3x}{x^2-9}\)
\(\Leftrightarrow\dfrac{18x+6x^2}{\left(x+3\right)\left(x-3\right)}\Leftrightarrow\dfrac{6x\left(x+3\right)}{\left(x-3\right)\left(x+3\right)}\Leftrightarrow\dfrac{6x}{x-3}\)