a: ĐKXĐ: \(x\notin\left\{\dfrac{1}{3};-\dfrac{1}{3}\right\}\)
\(\dfrac{3}{1-3x}=\dfrac{2}{1+3x}-\dfrac{7+5x}{9x^2-1}\)
=>\(\dfrac{-3}{3x-1}=\dfrac{2}{3x+1}-\dfrac{5x+7}{\left(3x-1\right)\left(3x+1\right)}\)
=>\(\dfrac{-3\left(3x+1\right)}{\left(3x-1\right)\left(3x+1\right)}=\dfrac{2\left(3x-1\right)}{\left(3x+1\right)\left(3x-1\right)}-\dfrac{5x+7}{\left(3x-1\right)\left(3x+1\right)}\)
=>-9x-3=6x-2-5x-7
=>-9x-3=x-9
=>-10x=-9+3=-6
=>\(x=\dfrac{6}{10}=\dfrac{3}{5}\left(nhận\right)\)
b: 4x(x-3)-3x+9=0
=>4x(x-3)-3(x-3)=0
=>(x-3)(4x-3)=0
=>\(\left[{}\begin{matrix}x-3=0\\4x-3=0\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}x=3\\x=\dfrac{3}{4}\end{matrix}\right.\)
