8)\(\Leftrightarrow\left(x+3\right)^2=\left(6x-3\right)^2\\ \Leftrightarrow\left[{}\begin{matrix}x+3=6x-3\\x+3=3-6x\end{matrix}\right.\\ \Leftrightarrow\left[{}\begin{matrix}x=1,2\\x=0\end{matrix}\right.\)
9) \(2x^2+7x-4=0\\ \Rightarrow\left(2x^2+8x\right)-\left(x+4\right)=0\\ \Leftrightarrow2x\left(x+4\right)-\left(x+4\right)=0\\ \Leftrightarrow\left(x+4\right)\left(2x-1\right)=0\\ \Leftrightarrow\left[{}\begin{matrix}x=-4\\x=\dfrac{1}{2}\end{matrix}\right.\)
10) \( \Leftrightarrow\left(x^3+x^2\right)-\left(x^2+x\right)-\left(6x+6\right)=0\\ \Leftrightarrow x^2\left(x+1\right)-x\left(x+1\right)-6\left(x+1\right)=0\\ \Leftrightarrow\left(x+1\right)\left(x^2-x-6\right)=0\\ \Leftrightarrow\left(x+1\right)\left[\left(x^2-3x\right)+\left(2x-6\right)\right]=0\\ \Leftrightarrow\left(x+1\right)\left[x\left(x-3\right)+2\left(x-3\right)\right]=0\\ \Leftrightarrow\left(x+1\right)\left(x+2\right)\left(x-3\right)=0\\ \Leftrightarrow\left[{}\begin{matrix}x=-1\\x=-2\\x=3\end{matrix}\right.\)
