a: \(A=2+\dfrac{8x\left(x+3\right)}{\left(x-3\right)^2}:\dfrac{x^2-9+2x+15-x^2}{x\left(x-3\right)}\)
\(=2+\dfrac{8x\left(x+3\right)}{\left(x-3\right)^2}\cdot\dfrac{x\left(x-3\right)}{2\left(x+3\right)}\)
\(=2+\dfrac{4x}{x-3}=\dfrac{5x-3}{x-3}\)
b: A>0
=>x>3 hoặc x<3/5
c: |A|=3-3x
=>(5x-3)/(x-3)=3-3x hoặc (5x-3)/(3-x)=(3-3x)
=>5x-3=3x-3x^2-9+9x hoặc 5x-3=9-9x-3x+3x^2
=>-3x^2+12x-9-5x+3=0 hoặc 3x^2-12x+9-5x+3=0
=>\(x=\dfrac{17\pm\sqrt{145}}{6}\)
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