a: \(\Leftrightarrow\left(x-1+2x+3\right)\left[\left(x^2-2x+1\right)-\left(x-1\right)\left(2x+3\right)+\left(2x+3\right)^2\right]-\left(3x+2\right)\left(9x^2-6x+4\right)=0\)
\(\Leftrightarrow\left(3x+2\right)\left(x^2-2x+1-2x^2-3x+2x+3+4x^2+12x+9-9x^2+6x-4\right)=0\)
\(\Leftrightarrow\left(3x+2\right)\left(-6x^2+15x+9\right)=0\)
\(\Leftrightarrow\left(3x+2\right)\left(-2x^2+5x+3\right)=0\)
\(\Leftrightarrow\left(3x+2\right)\left(-2x^2+6x-x+3\right)=0\)
\(\Leftrightarrow\left(3x+2\right)\left(x-3\right)\left(-2x-1\right)=0\)
hay \(x\in\left\{-\dfrac{2}{3};3;-\dfrac{1}{2}\right\}\)
b: \(\Leftrightarrow\left(x^2-4x\right)^2+4\left(x^2-4x\right)-2\left(x^2-4x\right)-8=0\)
\(\Leftrightarrow\left(x^2-4x\right)\cdot\left(x^2-4x+4\right)-2\left(x^2-4x+4\right)=0\)
\(\Leftrightarrow\left(x-2\right)^2\cdot\left[\left(x-2\right)^2-6\right]=0\)
hay \(x\in\left\{2;\sqrt{6}+2;-\sqrt{6}+2\right\}\)